Marrow is a fourteen-year-old prodigy at FIST (Fantom Institute for Superheroes-in-Training). With a perfect score on his finals, the ability to smash through walls, and leaps that can launch him over a city block, the Sidekick Internship Program is bound to place him with a top-notch superhoro mentor for the summer. But when a series of disastrous events land Marrow on academic probation, he is forced to team up with Flex - a drunk, hippie bum with the power of elasticity. The two Supers' powers and personalities clash as they are forced to overcome their differences to prevent the return of Cosmo City's most notorious foe, a supervillain so powerful, no one will survive the cataclysm he is sure to unleash.