Chaos is at it again, and this time it has a new plan: infiltrate the senshi from within. It has sent four of its minions to possess the Inner Senshi (Venus, Mars, Mercury, and Jupiter), hoping to set a trap to capture Usagi.

When the Inners are not transformed and are just mundane girls, the demons within them are inactive, and they have no idea that they're even possessed at all. However, when they transform, Chaos's minions immediately take over, causing them to behave like any enemy of the Senshi would. Their first goal is to eliminate the Outer senshi (Uranus, Neptune, Pluto, and Saturn), and then Usagi will be alone and more easily captured.

The plot begins thusly: The outers have noticed that the inners have been acting weird lately (the Inners sense something is weird with them in their minds, but can't figure it out since they don't know about the demons possessing them. They begin to act paranoid, more easily set off, and more unlike their true personalities, and this is what the outers think is weird), and have talked amongst themselves about it. While Usagi is on a weekend trip with Mamoru, a mysterious fire breaks out (one of Chaos's non-Innersenshi minions set it to get the Inners to transform), and all the senshi go to investigate. Unfortunately, the Inners transform, and all hell breaks loose. Now the remaining senshi must figure out what is going on and how to save their friends from the demons inside them (hopefully without killing them first).