This episode is quite unusual in that it takes several plot elements from the manga/anime and wraps them around an original story that feels like a filler episode, even though this episode contains crucial plot developments and couldn't possibly be called filler. This episode also contains some interesting ideas that are unique to PGSM.

The most important plot development in this episode was Mamoru discovering Usagi's identity. I was surprised (and actually a little disappointed) that this happened so suddenly in an episode like this. In the manga, we are not shown exactly when he figures it out, but he begins to cotton on as early as Act 3, or possibly even earlier since we are later shown in the manga that being transformed does not hide the characters' identities. We know for sure that he is aware of Usagi being Sailor Moon in Act 5, when he goes to Usagi's house and wakes her up so she can rescue Makoto. In the anime, Mamoru seemingly had no idea until episode 35, a Big Important Episode that contained many major plot developments (and is probably my favourite episode of the entire anime).

Incidentally, the handkerchief is inspired by the manga, where in Act 4 Usagi accidentally dropped her handkerchief at the masquerade ball, and Tuxedo Mask picked it up. I think it's a shame that PGSM didn't use subtle ideas like this to have Mamoru learn Usagi's identity, but oh well.

The other element that to an extent borrowed from the anime and manga was Usagi showing an interest in Motoki. In the manga, both Usagi and Makoto had crushes on Motoki, although this never became that big a deal. In the anime there were several filler episodes that basically revolved around these crushes. In this episode of PGSM, Usagi is only interested in Motoki because she thinks he's Tuxedo Mask. She thinks that the reason Motoki acts so differently to Tuxedo Mask (read: Why Motoki is so dumb) is to hide his identity. Evidently she's deluding herself.

The three Dark Kingdom henchmen that we've been introduced to are all still alive, which as you've probably gathered already, is unique to PGSM. This allows for some interesting interaction between them... Nephrite in particular seems to have serious attitude problems. The animosity between these characters does seem to have some very minor basis in the manga. Although the anime did have conflicts between them, they were all very different characters in the anime. Brand new to PGSM is Zoisite's fixation on Sailor V, and his mission to kill her. As a side note, I continue to find Queen Beryl much more organised than her anime and manga counterparts.

Finally, another PGSM-original plot development is Sailor V's warning that Usagi should stay away from Tuxedo Mask. At first this seems to be related to her knowledge that Tuxedo Mask is a jewel thief, but at the end she makes a comment about destiny, which suggests that she is aware to some extent of the past that Luna has not yet revealed to the Sailor Guardians.

As I said, this episode is pretty much entirely original plot, so there's not much to say other than this. This episode was fun (loved Takai and his hiccups), and had some interesting ideas in it, but it wasn't among the best episodes so far.