Marrow is a fourteen-year-old prodigy at the Fantom Institute for Superheroes-in-Training. To be paired with a top-notch Superhero mentor for the summer, Marrow has to get a perfect score on the Final Challenge. However, a series of disastrous events lands him on academic probation, and he ends up being paired with Flex—a drunk, hippie bum with the superpower of elasticity. Powers and personalities clash as the two Supers struggle to overcome their differences and work together with Marrow’s friends to prevent the return of Cosmo City’s most notorious Supervillain: Marrow’s estranged father, Spine.