After Bonnie tells Kim that cheerleaders should date athletes only, Ron fears that Kim may dump him and joins the football team; Professor Dementor seeks a way to overcome Kim's new indestructible battle suit.
Ron's having "letting go" issues when he has to pass on the role of the Middleton Mascot to Kim's brothers. Kim learns that a green-skinned, energy blasting woman just broke Dr. Drakken out of prison... but it's not Shego?
Camille Leon impersonates Kim to steal the designs for Club Banana's fall fashion line; Ron and teacher Mr. Barkin's acrimonious relationship continues outside school when they find they are also co-workers at Smarty Mart.
The villainous Electronique turns Shego's formerly heroic brothers evil, but Shego herself winds up turned from evil to good, resulting in her joining the faculty at Middleton High and becoming Kim's friend.
Kim's class trip to the beach gets a change in destination when Mr. Barkin books them to Ft. Mystic Cove Haven, a historical re-enactment town where all modern technology is taboo. Dr. Drakken finds a genuine pirate treasure chest, with a genuine pirate ghost inside!
Kim and Ron begin to suspect that there's something unusual about Ron's adopted baby sister, Hana. Meanwhile, Monkey Fist enlists the aid of an evil entity known as The Yono to hunt down the Yamanuchi School's secret weapon, "The Han."
Obsessed with his inability to steal Kim's indestructible battle suit, Professor Dementor sends his henchmen to kidnap "that boy who hangs out with Kim Possible but doesn't look like he belongs with her." But instead of Ron, they end up with Kim's nerdy Cousin Larry, who she reluctantly agrees to distract while the rest of the Possible family prepares a surprise birthday party for him. To make matters worse, Larry is convinced that his kidnapping is a role playing game, and is oblivious to the dangers that he's facing... or could cause, while under Dementor's custody.
As Graduation Day approaches for Middleton High, Drakken fumes that he's due for a win, Ron panics at the thought of all the changes to come, and Kim tracks down the source of mysterious markings appearing in fields all over the world.