Mourning the death of Prue, Piper and Phoebe must now come to grips with the loss of their older sister, and the loss of The Power of Three.
However, The Source discovers discovers an unknown sister and destiny - the daughter of Patty and her Whitelighter Sam. Paige the youngest Halliwell (can Orb and Telekinetically Orb objects to her) must restore The Power Of Three and reunite with her sisters as Witches before The Source's messenger Shax kills them.
Paige takes the Book of Shadows into her work to cast spells which help her co-workers. However she is unaware of the potenial consequences of her actions. Meanwhile Piper is filled with anger and rage over the death of Prue and the recent actions of Paige, and is possessed by a supernatural band of vigilantes known as Furies.
While makin a potion Paige wishes to have a life like Phoebe and they inadvertently switch bodies. While they cover the switch up so Piper doesn't get angry, Piper find herself involved with a Chinese Zen Master. His student, Yenlo, has turned to the dark side and has been killed by the Master's daughter, but is managing to stay alive in another plane called Limbo.
Piper, Phoebe and Paige are shrunk to a height of five inches when they walk into a trap set by a demon named Gamil, who wants to burn woman in his kiln for his doll collection.
Paige accidently summons a medievel knight, who believes Paige is the love of his life. However, the knight is under the influence of an evil sorceress who looks just like Paige but is really her past life.
The Source sends Piper into a deep coma, where she percieves an alternate reality. Phoebe and Paige must find a way to return her reality and save her from reading a spell to give up their powers while she is delusional.
Cole must face his true demonic nature when he is faced with another demon who is mistaken as the murderer of local witches who belongs to the same coven. Meanwhile, Cole proposes to Phoebe, and Piper and Leo must consider their future involving children.
The Halliwell sisters must find a way to release the Muses which have been abducted by a Warlock who is attempting to build an evil faction in the absence of The Source.
While Phoebe performs jury duty in a murder case, she is hit with a Premonition about the real killer, and must convince the rest of the jury that the defendant is not guilty. The problem is the only way to do this, is to prove the existence of magic. Meanwhile, Piper, Leo and Paige try to help Phoebe find the real murderer, but they stumble upon a gang of demons (Rat Demons) and they must solve the crime and keep Paige's friend out of danger before Phoebe gets thrown off jury.
With Leo as her guide, Paige goes back in time in her teen years, in an attempt to resolve her feelings about the accident that killed her parents. Meanwhile, Piper must prevent ghosts, who have inhabited Cole and Phoebe's bodies, from fullfilling their mission.
The Source breaks an old-age agreement between good and evil by stealing The Hollowm, an anicent vapor which he uses to absorb first Piper's and then Paige's powers. Phoebe must allow Cole to help The Charmed Ones inspite of having a Premonition that involved Cole sacricifing his life to save her from evil as Phoebe tries to battle The Source with her powers to protect her sisters. But there may be more to the Premonition Phoebe just can't see.
Wanted to protect a ten-year-old oprhaned boy who is a firestarter, Piper and Leo try to hunt down the demon bnefore he can deliver the kid to The Source. Meanwhile, Phoebe is given Gram's wedding ring by Cole, but to their surprise Gram's cursed the ring to transform the wearer into a traditional 1950's suburban housewife.
Phoebe develops a case of cold feet over marrying Cole and casts a spell which brings a young innocent Phoebe and an old cynical Phoebe to the manor to help make a decision. Meanwhile, Cole is horrified to find that The Source is taking over his entire being, The Source's chief rival, who believes The Source is dead, is convinced by
The Seer to kill The Charmed Ones in order to earn the allegiance of the entire underworld.
As Phoebe prepares for her wedding day, she is completely unaware that The Source has taken over Cole's body, a plot that will likely ruin the big event. Meanwhile, The Seer tells The Source that if he can marry Phoebe in the "dark-way", it will insure that their future son, will be the most powerful, evil being ever.
When two ghosts from Leo's past return to seek revenge, Leo faces his demons by submitting, causing Piper's life to be threatened, leaving Paige to deal with the situation. Meanwhile, Cole tried to convince Phoebe they need a home of their own.
Amongst newlyweds, Phoebe and Cole and already-married, Leo & Piper, Paige beings like a fifth-wheel but she continues her suspicions about Cole. Meanwhile, The Source plots to impregnate Phoebe with her evil spawn.
Phoebe tells Piper and Paige that she is pregnant, and that Cole is the father. Meanwhile Piper and Paige team up with a wizard to stop a coronation of the new Source, unaware that it's Cole and Phoebe is soon to be the Queen of the Underworld.
A vampire queen tries to dethrone Cole as ruler of the Underworld and attempts to turn Paige against her sisters. Meanwhile, Phoebe starts to feel under the weather.
Phoebe accepts her new role in Cole's life, but she still sets out to save an innocent after she has a Premonition and even seeks her sister's help in protecting the man. Meanwhile, Piper's heart doesn't seem to be in it as she prepares to defends her family against any new threats from the Underworld.
The Seer plans to steal Phoebe's unborn baby so she can raise the child to become the next Source and prevent the throne from passing on to another demon. Meanwhile, the baby begins to take over control of Phoebe's body, which proves dangerous for Paige because she's half good with Whitelighter blood.
When the Angel of Destiny offers the sisters a chance to relinquish their powers and lead normal lives as a reward for vanquishing The Source of all Evil, their decision is put on the back burner, while they try and avoid an FBI agent who has them under surveillance and deal with Cole's calls for help, who is trapped in another realm, holding on to his love for Phoebe.