A tussle in a scientist's lab causes "modulators" to accidentally attach to both Kim and Shego.  Unaware of the microchips' presence, Shego and Kim find themselves whirling from one emotional extreme to another while their rattled companions, Drakken and Ron, try to make sense of their bizarre behavior.

Ron arrives at the opinion that "bad boys" get the girls. As he prepares to test this hypothesis, a mishap with Drakken at a villains convention causes Ron to become pure evil, while Drakken can't help but do nice things. Before Kim can realize what has happened, Ron takes Drakken's place and Shego is sure that this time she's hooked up to a villain with actual potential.