When Stan divides the Superheroes into duos to face the notorious Dr. Dark, the competitors attempt to prove that they are better superheroes than sidekicks. Their quest for Dr. Dark requires them to survive the scariest roller coaster imaginable while keeping their wits about them. But later the heroes turn on each other when a note is discovered at the Lair that implies that one of them is a mole. The action culminates in the most shocking elimination ever.