Twins Phoebe and Max are enjoying their superhero lifestyle, but when one 'save' goes awry, the Thundermans are sent back to Hiddenville. While Hank and Barb enjoy their return, and Billy and Nora look forward to a normal high school life, Max and Phoebe are determined to regain their superhero status.

When Chloe develops a destructive new superpower, the Hero League orders her to an elite boarding school for superheroes to learn control of her abilities. Faced with the prospect of sending Chloe away for years, the Thundermans split apart, with Phoebe, Barb and Billy taking her into hiding. Max, Hank, and Nora track their rogue family members, until the two factions face off against each other in a full-on battle for the Thundermans’ future.