The episode opens in a hotel room. One man is brushing his teeth while another man wearing a hat, scarf, and sunglasses is rummaging around in the other room. The TV is showing the begining of the festival of lights which is being held nearby. The man with the toothbrush is chatting amicably with the other until he notices how much of a mess the man has made. The brusher wonders aloud why the man made such a mess just hunting for a wallet, and then is shot dead by his friend. The killer flees the room and tosses his hat, scarf, and glasses away into the river.
Meanwhile, Conan goes along with Rachel and Richard to the festival of lights to try and have a little fun. Conan isn't enjoying himself because Rachel is treating him like a little kid, even going as far as buying him a rabbit balloon. During the last part of the festival, when the last of three lighted words is lit, they meet a man who asks Rachel to take a picture of him in front of the lights with a disposable camera.
The man turns out to be a famous writer named Nicodemus who is there on a writing assignment. Rachel, a fan of his, agrees to help Nicodemus by taking pictures of him around the festival. Their fun time is abrubtly ended when the local police inspector, Inspector Worthington, arrives and accuses Nicodemus of killing his writer friend Salvadore Emerson. They all go to the crime scene and find Emerson laying on the ground, his toothbrush laying nearby.
The inspector is certain that Nicodemus was the killer, but Richard sees the man's empty wallet and messy hotel room and decides that this was just a robbery. Nicodemus, on top of that, has an airtight alibi. He has pictures of himself with the first of the three lights at the festival, meaning he couldn't have been at the hotel room at the time of the murder. Conan, however, isn't fooled and knows that the smug Nicodemus had to have committed the murder. His suspicions are concreted when someone from the magazine Emerson wrote for comes by and is forced to hire Nicodemus to meet Emerson's deadline.
Conan studies the evidence carefully, but he is stumped as to how Nicodemus could have done it and been at the festival so early. When it finally hits him he has to act quickly, Nicodemus is already trying to leave and Inspector Worthington is having a hard time stopping him with no evidence. Conan uses his newest gadget from Dr. Agasa, a wristwatch that shoots stunning needles, to put Richard to sleep. Conan then hides behind the unconcious Richard and uses his voice changing bowtie to explain why this was no simple robbery.
Conan points out that no one would be brushing their teeth with a stranger around. He then tells them that the robber wouldn't have had time to mess up the room after shooting Emerson. With only the alibi left unexplained, Conan attempts to draw attention to the pictures. His plan is almost ruined when Rachel sees his balloon floating behind Richard, but he manages to show the inspector the final clue. In the picture Nicodemus has a unbroken dark tan, but now Nicodemus has a white band on his wrist where he was wearing a watch. It turns out that the picture was taken a year ago at the last festival. Nicodemus finally confesses and is carted away to jail, while Richard is congratulated on another successful case solved.
Conan is hanging out with Amy, Mitch, and George, listening as they discuss the upcoming soccer finals. He soon gets bored from all the soccer talk and goes home from school, only to find a high school girl at the Moore's door. She is hesitating about going inside, but Conan ushers her in to see what's wrong. The girl, Riana, comes in and explains that she is looking for her missing boyfriend, Jimmy Kudo.
Rachel is furious, and Conan is justifiably confused, since he doesn't even know who this girl is. Right at that time Dr. Agasa happens to call Conan to see how his newest gadget is doing, but Conan pretends that it is Jimmy. Conan gives Riana the message that Jimmy will call her later, further infuriating Rachel. Riana decides to go on home, and Rachel follows to give Jimmy a piece of her mind. Conan, as usual, tags along.
When they get to Riana's house, Conan quickly sees that something is wrong. The keylock is scratched like someone has broken in, there are only men's and boy's shoes in the closet, and Riana doesn't seem to know where anything is kept. He goes exploring and finds a totally ransacked room with the name Matthias on the door. Conan happens upon a picture of a young man and a boy in the room and concludes that the little boy is Matthias. After watching some of the soccer final in the other room, Conan realizes that the star player for the Southside spirits, Harrison Akers, is the man in the picture. While Harrison is usually a great player, he makes error after error as they watch.
Finally figuring out what is going on, Conan goes into the bathroom with his newest gadget, all encompassing phone fax machine lunchbox. He uses his voice changing bowtie and calls Riana to tell her that he knows Matthias has been kidnapped and that Harrison has been forced to throw the game. Conan also tells her that he knows she just pretended to be his girlfriend in order to find him to help with the case. He then gets Riana to fax him the details of the case and the ransom note. Things take a turn for the worse when Rachel grabs the phone and begins shouting at Jimmy. She hears her voice coming through Conan's phone and starts hunting the house for Jimmy. Conan, safe in the bathroom, studies the faxes. The note, found that morning, just says "brother revive matthias." Conan is stumped as to the kidnapper's identity, and goes out to watch some more of the game. After Harrison accidently helps make a goal, they recieve a fax saying "You've broken your promise, dont expect to see your brother again."
Conan goes back to searching for clues in Matthias's room, and finds a newly released game called Hero's Quest. He loads the game and finds that the characters have been named Matthias and Nicholas. Conan figures out that the note earlier was a reference to this game and goes back into the bathroom to call Riana again. He asks her if she knows a Nicholas, which she does, since it is a recently injured teammate of Harrison. Conan tells her Matthias must be with Nicholas, and he is going there to get him back. This time Rachel tracks down Jimmy's voice and corners him in the bathroom. Conan tricks Rachel into turning around while he rushes out. When Rachel finds him around the corner, he tells her Jimmy just ran by. Riana calls to tell Harrison that Matthais is safe, and they then go to Nicholas's house to find Jimmy and Matthias.
They arrive at Nicholas's house and an angry Rachel kicks down the door when they arrive. They find Matthias happily playing video games there, and Nicholas admits that he made it look like a kidnapping so that Harrison would know some of the pain Nicholas felt being out of the limelight. He also blames Harrison for the leg injury that kept him out of the games for three months, but is ashamed to hear the victorious Harrison thank Nicholas on the tv.
After they notice Jimmy is not there, they call him to see what he is doing. The phone goes off in Conan's backpack and he runs off into a nearby ally. Rachel follows him most of the way, but stops after he tells her that this will all be over soon, but he cannot tell her what is going on yet. Using car lights and a block to stand on, he creates Jimmy's silhouette and tells her not to cry. The car turns out to be Dr Agasa's, who hides Conan and tells Rachel that Jimmy just ran past. As the episode wraps up, Rachel finally believes Riana's story that she lied about being Jimmy's girlfriend and just needed to find him to save Matthias.
Richard recieves a mysterious note that says, "The next night of the full moon, shadows will begin to disappear from Moonlight island. Please Investigate, Kasper Austin." They then recieve a call from Kasper Austin saying $5000 dollars have been deposited in Richard's bank account and wishing them good luck on Moonlight Island. Seeing as they have already been paid, Richard, Conan, and Rachel take a ship out to the nearby Moonlight Island and try to find Kasper Austin.
Once they arrive, however, they learn that Kasper is dead and has been for 12 years. He was a concert pianoist who went mad after playing one last concert on the island. He went home and set his house on fire, then stabbed his family to death. As the house burned down around him, he died playing Beethoven's Moonlight Sonata. Wondering who it was who hired them, they decide to go ask the Mayor of the island. On their way downtown, they meet the local doctor, Nadia Adams. She tells them that she is originally from the city, but moved to the island for the peaceful small town life. She then directs them to the community hall, where the Mayor and many others are gathering.
At the community hall they find that everyone is there for a memorial service being held in honor of Mayor Kirkpatrick, the former mayor who died two years ago of heart failure. After finding a dusty piano in one room, they are told by Kevin Hadley, the current mayor's assistant, that the piano is cursed. It was at this piano that Kirkpatrick was found dead two years ago at, right after the song Moonlight Sonata was heard. Kevin says that the piano hasn't been touched since then, but Conan plays a few bars on it and determines that someone is keeping it tuned. They soon meet some of the people at the memorial. All 3 of the mayoral candidates are there: Theodore Kinsella, the current mayor, Henry Kavanaugh, and Matthew Shumacher. They also see Rene Kinsella, the mayor's daughter, Steven Mulholland, her fiancee, and Ken Nicholson, a friend of Kirkpatrick. They learn that Ken Nicholson has been a very scared and secluded man ever since Kirkpatrick died.
An hour or so after the memorial starts, Mr. Kavanaugh leaves to go to the bathroom. Soon after the Moonlight Sonata is heard playing. They rush to the piano room to find Kavanaugh draped dead across it. It is obvious from the evidence that he was drowned in the sea outside, then drug in and propped up on the cursed piano. A tape player is quickly found to be the source of the music. Since the front door was watched, they determine that someone at the memorial must have killed Mr Kavanaugh. Conan finds the sheetmusic to the Moonlight Sonata laying on the piano, and Rachel discovers there is an error on the fourth line. Conan decides that the note they recieved means that there will be more murders.
Richard, Rachel, Conan, and Dr. Adams all decide to stay the night at the community hall to keep an eye on the crime scene. As they sit, they discuss the murder of Kirkpatrick two years ago. Nadia confirms that he died of heart failure, but says he was found with a terrified look on his face, and that one of the windows were open. They spot someone lurking outside the window at this point, but the prowler gets away from them.
In the morning Inspector Meguire arrives from the city and takes over the investigation. After having his forensic team take over the crime scene, he has all of the 38 people who were at the memorial service come to City Hall for questioning. As the day wears on, Conan studies the few people who still haven't been questioned. The most suspicious man is Ken Nicholson, as he seems scared stiff and won't answer any questions. After he is released, Ken continues hanging around, eventually going upstairs. Conan follows him as the second measure of the Moonlight Sonata starts playing on the pa system, only to find Ken standing shocked at the entrance to the pa booth. Inside Mayor Kinsella is found dead, sitting in a chair with a knife in his back.
Dr. Adams checks Mayor Kinsella's body and determines that he has only been dead for a few minutes. Nearby they find some music written on the floor in blood. While Conan is looking at it he gets shoved out of the way, only to fall directly into the blood. They are relieved to see that the blood has already dried, so Conan hasn't smudged it. Taking into account the time of the death, they rule out Rene Kinsella because she was in questioning and Dr. Adams because she was sitting with Conan and Rachel at that time. Ken Nicholson, Kevin Hadley, Matthew Schumacher, and Steven Mulholland are the suspects who do not have an alibi at this time. Nicholson claims he merely went upstairs because Kinsella asked him to meet him there earlier.
Conan struggles to figure out if the music left form some sort of coded message. With Rachel's help he figures out that each key on the piano stands for a letter of the alphabet. Thus the sheetmusic left with Kavanaugh reads "The killing has just begun," and the music written at Kinsella's murder said "The firestorm grudge has been avenged." Conan is sure that another murder will soon occur since there are three movements in the Moonlight Sonata, and only two have played so far, one at each of the two murders.
After learning from the local police officer that some of Kasper's sheet music survived the fire in a safe, Conan is eager to see if it too is a coded message. As the officer searches for the key to the safe holding the old papers, Conan finds out that there were only four witnesses who actually saw Kasper kill his family and burn his house down. They were Kirkpatrick, Theodore Kinsella, Nicholson, and Kavanaugh. Realizing that the community hall, where the papers are stored, is now empty, Conan rushes back to the hall. They hear the third movement of the Sonata playing, and rush to the piano room. Inside they find Mulholland laying on the ground unconcious and someone under the piano. In the darkness the other person escapes through a broken window and flees.
They then find Ken Nicholson hanging dead in the storage room. Near him is a piece of sheet music that says he committed suicide and killed the others to cover up his criminal activities. Seeing that Nicholson had no chair to stand on for the hanging, Conan knows that this was no suicide. He remembers the man underneath the piano and looks for himself under there. Conan finds a secret compartment that is has some white powder still in it, which he identifies as a narcotic. He also finds a piano tuning hammer next to the unconcious Mulholland. As everyone is gathered together again, Conan notices that Hadley's hand is bandaged. He follows Hadley outside and notices some white powder on the man's coat. He also finds that Hadley is carrying a wallet full of foriegn coins.
At this time the police officer finally finds the sheet music Kasper Austin left behind 12 years ago. Translating it, Conan discovers it begins, "To my beloved son, Simon." He learns from the officer that Simon Austin, Kasper's son, was a sickly boy who was in the hospital when his family died. With all the details now in place, Conan now knows who the murderer is.
Conan rushes upstairs and finds that the Reverse light on the PA system's tape player was on during the murder. Richard, who followed Conan upstairs, gets put to sleep by Conan's stun gun watch. Conan then uses his voice changing bowtie to address everyone over the PA speakers. Conan explains that Kevin Hadley spread the story about the piano being cursed because he hid narcotics in it and carried on drug deals in that room. Hadley hurt his hand the night before when escaping through the broken window. Mulholland was merely there to tune the piano because he adored Kasper's music. As for Kinsella's murder, he was actually killed at least a half hour before he was found, since the blood on the floor had had time to dry. Conan then announces that the Kinsella murder tape was reversed to 5 minutes from the begining. He explains that only a man could have dragged Mr. Kavanaugh's body in from the sea, so the murderer has to be a man.
Conan then reveals that the murderer is Dr. Nadia Adams, who is actually Simon Austin, Kasper's son. When Simon examined Kinsella earlier, he lied about how long Kinsella had been dead to give himself an alibi. Conan then revealed that all of the four men who had died had used Kasper Austin's worldwide concerts to smuggle narcotics. When Kasper wanted to stop they locked him and his family inside his mansion and burned it down. Simon, who was in the hospital at the time, survived and was taken in by a foster family named Adams. He pretended to be a woman when he returned to the island two years ago to fool everyone and seek information about his family's deaths.
As Conan finishes his explanation, everyone finds that Simon has escaped. Conan knows where he is going and rushes to the community hall. Simon is inside playing the Moonlight Sonata on the piano as the hall goes up in flames. He admits to Conan that he caused Mayor Kirkpatrick to have a heart attack two years ago by admitting his true identity. It was then that Simon decided to kill the other three using the Moonlight Sonata theme. Simon knows that he is now a murderer, just as the four men were, and refuses to leave the burning hall. Simon then grabs Conan and throws him out the window, saving Conan's life. The flames grow higher as music comes from the engulfed hall. Later, as they are going home, Richard and Rachel ask Conan what the last music meant in code. He replies that he doesn't remember, but to himself he thinks, "Thank you, little detective."
Conan is out playing hide and go seek with George, Mitch and Amy in the park. Conan is it and easily finds George hiding in the trash. He cites how there is no perfect crime, and George has left many clues to where he is hiding, the most obvious of which is George's clearly visible rear. Conan laments that he wanted to go to the University's Music and Arts Festival today with Richard and Rachel, but got roped into this game instead. After finding George, Conan's turn is over and he uses his newest gadget to call everyone back. Dr. Agasa has created small badges for the four that say Detective Boys on them (Detective Boys is what the Junior Detective League was originally called before it was dubbed.) The badges are actually powerful transcievers that allow them to communicate with each other.
Now that George is it, everyone runs off to hide. Conan chooses to hide in the lap of an elderly man napping behind a newspaper. Conan reads a bit of the paper while he hides and sees that serial killer have kidnapped a young girl. Conan is suprised when Amy sneaks up from behind and says that since cute girls have been kidnapped, she must be next. Amy then says she knows that if anything ever happened to her, Conan would do anything in his power to rescue her. She also says that someday their destinies will become one and runs off to hide. George hears their voices and finds Conan. He then finds Mitch hiding in some bushes. Conan takes some time to mess with yet another gadget from Dr. Agasa, a skateboard with a solar powered engine.
Meanwhile Amy has found what to her is the perfect hiding spot. A car parked next to the road has its trunk slightly open. She climbs inside and hides. A couple of minutes later a couple of men come to the car, put some items in the trunk, and drive off with Amy still inside. The three boys hunt for Amy for a long time, but cannot find her anywhere. Finally they attempt to contact her with the radios. Amy wakes up and answers, explaining she fell asleep in the trunk underneath a blanket. She is scared but Conan calms her down so that she can give them some clues as to where she is. She soon finds a bag full of money and a saw with something slimey on it. She almost looses it when she finds a severed head in another bag. She screams, but the driver just thinks that the screaming is from a nearby amusement park.
Conan figures that this must be the kidnappers he read about earlier. Amy says that the car is stopping alot and there is alot of noise. Conan thinks and remembers that the only road currently under construction is in the financial district. He is chilled when he hears the voices of the driver and his companion. One says that he didn't have to kill the girl after they got the ransom money, but the other says he had to kill her since she saw their faces. Noting that they only have 3 hours until sunset, Conan, Mitch and George set off on the skateboard to find the car. Conan figures that the Baker Street Bridge will be roadblocked by the police hunting for the kidnappers, so they will not drive that way. He circles around to where he thinks they will be and waits.
Five minutes pass and no car. There is no response from Amy either. George suggests the car might be in the Baker Tunnel, but Conan knows that they would have had to get through the roadblock for that. He figures the car must be in a thick building. Amy suddenly responds and says there was a loud humming noise for awhile, which means she must have been in the tunnel. Now she says that they have pulled over at a shopping center, because she heard a bell and now hears liquid pouring. Guessing that they are at a gas station, Conan jets off to intercept the car. It passes them on their way and they turn to chase it. Just as they catch up the sun goes down and they begin to loose power. Snatching a nearby hose on the sidewalk, Conan manages to loop onto the car's antenna and use it to keep up with the car. He holds on tight, but the car almost shakes them with wild maneuvering. Just as Conan is about to let go, George graps on and pulls them up to the car. The car suddenly stops, leaving the three knocked down in the road.
The guys get out and are suprised to find Amy in the trunk. Conan, thinking they are about to hurt her, kicks a biker's helmet at the one holding Amy and knocks him out. Conan accuses the other man of being a murderer, but is shocked to see that the head was fake, just paper mache. The men were going to put on a play at the University Festival, and all of the stuff in the trunk was just props. The real kidnappers had already been caught by the police, explaining how the two got through the roadblock. Conan is embarrassed, but since they have knocked out one of the actors, they have no choice. The three boys stand on each other's shoulders and put on a coat and hat, pretending to be one of the murderers in the play. Amy, meanwhile, plays the part of the dead girl, since the fake head was damaged in the adventure.
Conan is at Dr. Agasa's house reading the newspaper. He is discouraged by all of the robbery, kidnappings, and murder, but Dr. Agasa reminds him that Conan can help make the world better. Dr. Agasa then shows Conan his newest invention, a pair of glasses that can track a homing device. Conan takes it excitedly and goes home, eager to try it out.
When he gets to the Moores' house he finds a girl named Michelle Hamlin there. Michelle wants Richard to help find her father, Kent Hamlin. He was a taxi driver who quit 1 month ago and disappered. She shows them a picture of him holding a cat. She explains that he had four cats, Tee, Per, Prose, and Iie. Thinking this will be a slow case, Conan goes to slip the tracking device on Rachel for a test, but accidently slips and puts it on Michelle's watch. He forgets about it after she leaves, and they get down to trying to find a clue.
Richard asks all around, but has no luck. Finally when they are watching horse racing on tv they hear the horse named Prosperity mentioned. Conan realizes that the four cats' names make up the word prosperity, so they go to the track to see if Kent is there. Sure enough they find him and reunite him with Michelle at his home. She hugs him tightly, but he looks a bit scared. The three leave but catch sight of a large man in a trenchcoat watching them.
The next day Kent is found hanging in his apartment and Michelle is missing. After learning that Kent was strangled by someone with big hands, they fear that Michelle has been kidnapped and possibly murdered. Conan has no idea how to find her until suddenly he remembers the tracking device he accidently planted on her watch. He takes off alone to follow the signal and ends up at a video game arcade. Inside he is looking for Michelle when he runs into a big guy who knocks him down, then kicks him out of the arcade. About this time Conan's glasses battery goes dead and he returns home.
Richard and Rachel are still sitting around thinking when he returns, but Rachel sees the man in the trenchcoat watching them through the window and gives chase, downing him by kicking through his car's window. The man turns out to be another detective, this one hired by Kent's brother, Aaron Hamlin, to find Kent. Conan recognizes a picture of Aaron as the man who knocked him down in the arcade and wonders if he killed Michelle and took her watch.
Conan goes to Dr. Agasa's house to recharge his tracking glasses and Dr. Agasa tells Conan not to be reckless, but instead to exhibit calmness, awareness, and carefullness, the traits of a good detective. He reminds Conan of a gaurd recently shot while trying to stop the robbery of 100 million from a cargo truck. Conan agrees and goes back home with the recharged battery to get Rachel and Richard. He leads them to a hotel by following the tracking device, but claims that he merely saw Aaron there one day. At the elevators they nearly run into a woman with a large number of suitcases, but do not pause long before going up to Aaron's room. In the rom they find Aaron with a can full of Potassium Cyanide in his hand. They also find a large number of empty aluminum cases laying in the corner of the room.
Seeing that the two of the three people are dead now, and Michelle and Aaron's stories didn't match, Conan realizes that they must be the three suspects in the recent truck robbery. Conan figures that Kent must have been the getaway driver and fled with the money afterwards, leaving the other two to hire detectives to find him. Conan then realizes the woman they ran across downstairs was Michelle in disguise and chases after her, only to see her quickly disapper into a taxi. Rachel and Conan race after them in another taxi and end up at the harbor.
Conan catches sight of Michelle talking to a man known as O'Brian. She tells him that she knows he set things up where her two accomplices would be killed, and that he has a reputation of killing all the people he has doing his dirty work. O'Brian demands the money from her, but she says she hid it. He claims that he knows where and prepares to shoot her. Conan manages to kick a float at O'Brian and Michelle is merely hit in the shoulder. Michelle sinks to the ground and tells Conan that she is tired, and explains all that happened, including how Aaron borrowed her watch because he broke his own strangling Kent. O'Brian makes one last attempt to shoot them, but Conan knocks him out with another float. At the end as she is about to be arrested, Michelle tells him, "Thanks for everything, little detective."
Conan, Amy, George, and Mitch are all at the river one afternoon catching fish when suddenly a remote control boat with a red balloon tied to it goes speeding past. Watching it, they are suprised when a shot rings out and the balloon is popped. Conan uses his binoculars to look for the shooter and spies a man with a rifle on a far away building. The shooter is surrounded by three guys with guns who appear to be holding him at gunpoint. They turn and leave with him, but as he turns, the shooter happens to see the reflection of Conan's binoculars.
Racing to the building, the four scour the area for clues as to what was going on. Conan manages to find a carefully hidden small calculator that has the number 3540405162 on it, and he decides it must be a clue left behind by the captive shooter. They quickly get Inspector Meguire to come out and take a look around, but he is skeptical of their story. He takes the calculator with him but isn't very concerned about the case.
Conan goes home and tries to puzzle out the number that was on the calculator. Richard thinks that they just made it all up, but Rachel trusts Conan and tries to help. She suggests that the 162 might by highway 162, and the rest of the numbers are just garbage. Richard happens to mention that a part of that highway resembles the bend in the river where the shooting happened, and the next day he is roped into carting the kids and Rachel to the highway to look for spots where the bend is the same. Conan finally finds a tall building where the bend is the same and they are certain this is where a shooting will soon happen.
When they arrive home they convince Richard to call Inspector Meguire and are suprised when Meguire asks Richard to come to headquarters with Conan. When they get there they learn that a police officer, Charles Mulligan, and his wife Erin have turned up missing. Considering that Mulligan was a former Olympic sharpshooter, they figure they are holding his wife hostage so that Mulligan will pull off an assasination for them. Meguire and Richard think that the shooting will happen the next day at the highway, but Conan isn't so sure. The rest of the numbers are still bothering him, but he cannot figure it out.
The next day the area is well staked out with police and even a hidden helicopter, but the time ticks down to 1 without any sign of the men. Sitting in the van with Richard, Meguire, Rachel, and the kids, Conan continues to struggle with the numbers. Mitch happens to type them into a calculator, and Conan finally understands. Reading the calculator upside down, it looks like 291ShohohSE. They figure out that the shooting must be targeting a train, the Shoho high speed express, on the 29th at 1, which is that day. Inspector Meguire rushes off to the helicopter and is suprised to find that Conan has snuck aboard as well. Meguire sticks a flight helmet on Conan and they continue on after the train.
On the train, a man radios to the other men that the target is in place. The target appears to be a man sitting in the front of the train with his wife and 2 kids. The scene shifts to a rooftop where Erin is being held at gunpoint by one of the men, while the other two keep an eye on Mulligan. As the train comes around the bend, the men urge Mulligan to shoot or they will kill his wife. Right before he shoots the police helicopter does a close flyby, scaring them. Mulligan takes the opportunity to knock the two closest men out with the rifle's butt, then stops because the last man is still holding his wife hostage. Conan sees the situation below and uses his powerful sneaker to kick the flight helmet at the last man. The man is knocked out, and the Mulligans are reunited.
The helicopter lands and the 3 men are taken into custody. The rest of the gang finally arrives, too late for the action. Richard scolds Conan and tries to bop him on the head, but about breaks his hand on Conan's retrieved helmet. They learn that the men were members of the Tiger Dragons gang, which was seeking revenge against a prosecutor for arresting their gang's leaders. Things are smoothed over when Richard takes the credit for the case, and the two decide to hit him up for a vacation. Asked where he wants to go, Conan says "The amusement park of course." To himself he dryly thinks, "It's never easy living the life of a little boy."
The four kids are all sitting around in class after school one day trying to think up a way to get a new case. While the three kids think up ways and Conan tools around with a soccer ball, a chubby kid comes running in asking if they are the Junior Detective League. The boy, Harry, says he has a missing person case for them, but they decline after learning it is just a missing cat. The boy offers to pay them a dollar each, but is unable to buy their services until he offers them 4 rare gold foil Masked Avatar trading cards. The three kids jump at the offer, and Conan finds himself on a cat hunt. They harass every cat in the area, but are unable to find his cat Akira. Finally they have Harry mimic the cat's meow, and they immediately hear an answering meow. The cat emerges from the window of a nearby house, but he is covered in blood. Seeing that the cat is not hurt, the four race over to the window to see what is inside.
They are shocked to see a dead man laying face first in the bathtub. They race off to a nearby phone booth and Conan calls Inspector Meguire. Meguire and some officers show up and finds Conan sitting on top of the booth watching the house. Conan tells him that no one has left or entered the house because he has been watching from there all this time. Meguire goes with them to the front door and bangs on the door. A mustached man answers the door and introduces himself as Hamilton Timberman. He scornfully claims that he was just taking a bath and there is no body, this is just a prank by the children. He gets grumpy as Meguire presses him and tells them to go ahead and search the house, but he is going to take a nap upstairs. He says as he goes that if they need anything, his brother will be home soon.
The police carefully search the house, but they are unable to turn up anything. The brother, Hadrian Timberman, soon shows up and seems suprised that they are there. Conan notices that a single leaf falls off of Hadrain's pants when he comes into the house. After George accidently breaks a vase, Hamilton's voice is heard saying, "Hey, keep it quit down there!" Hardrian explains that his brother, a writer, is a grumpy person. A couple of minutes later Hadrian picks up the phone and says that it is a wrong number, but Conan is sure that he didn't hear the phone ring. With Hadrian's permission they go upstairs to Hamilton's room and find him sleeping in a chair in front of a tv. They quietly search his room, but are unable to find anything. Noticing that there is a high wall around the house, Meguire thinks there is no way anyone could have gotten past Conan, but Conan points out a large tree in the back yard that could have been used. They find that there is only a narrow ledge on the other side of the wall, meaning no one could have snuck a body out that way. At this point Inspector Meguire is certain that the kids are playing a prank on him and leaves with his officers.
Conan knows what he saw and is certain that something is fishy here. As darkness falls he goes back around the house to the tree. He is suprised to find the three kids there also investigating. He notices as he climbs the tree that the the leaves are the same as the one that fell off of Hadrian earlier. He looks in the second floor window and sees that Hamilton is still asleep in the same position as before. He suddenly realizes where the body has been the entire time. Conan climbs down and tells the others to go call the police as he enters the house through the unlocked bathroom window. He locks the window behind him, making sure they do not follow him. Sneaking through the house, Conan catches sight of Hadrian putting a cell phone down. He slips by and goes upstairs and confirms his suspicions. Hamilton is sitting in the chair dead. As he is looking at the body, Hadrian hears him and comes upstairs with a golf club. Conan hides but is given away when George's voice rings out over the radio badge. Seeing that the jig is up, Conan leaves his transciever on and stands before Hadrian.
Conan tells the man that he is a detective and has figured out exactly how Hadrian tried to get away with the murder. Conan remarks that this is the first time he's ever seen a dead body watching tv. He says that Hadrian had hidden the body upstairs before the police arrived, then disguised himself with a fake mustache to look like Hamilton. He then answered the door and pretended to be his brother, then went upstairs to his room. Hadrian then climbed out the window and used the tree to get over the wall. He then snuck off along the ledge and came home as himself, Hadrian. The yelling that was supposedly from Hamilton upstairs was actually recorded on the answering machine by Hadrian and activated with his cell phone. The wrong number earlier was just Hadrian erasing the message.
Meanwhile, the kids have gotten Inspector Meguire on the phone, but he does not believe them and doesn't want to waste any more time listening to them. Just before he can hang up Amy sticks her radio badge up to the phone, letting Meguire hear Hadrian and Conan's conversation. He finally believes them and rushes to get officers out there.
Back in the house Hadrian is trying to hit Conan, but Conan runs from him. He is almost cornered in the bathroom, but Hadrian slips on the soap and Conan escapes to the kitchen. Conan sees that Hadrian has once again assumed his Hamilton disguise and realizes that he is out of his mind. Hadrian begins ranting about what led him to the murder. He worked in a securities company and was confronted by Hamilton about some insider trading that Hadrian was involved in. Hamilton threatened to expose Hadrian unless he financially supported him. Hamilton became lazy and stopped writing, ruining Hadrian's vision of him as an ideal writer. Hadrian, in his insanity, wanted to become his brother and become the success his brother should have been.
Conan finally manages to knock Hadrian out with a kicked tea kettle. The cops finally arrive and arrest Hadrian, and the Junior Detective League has their honest reputation restored. They find themselves sitting around bored again soon enough, even though the boy Harry has lost his cat again. The cat comes home on its own this time, leaving the four to look for other cases to solve.