An uneventful day at school until the powerful Book of Legends is suddenly stolen from Super Hero High. In order to uncover the mystery, Wonder Woman, Batgirl, Supergirl, Bumblebee (comics) and the rest of the Super Crew must journey through the depths of the ocean to Atlantis (DC Comics). There, the girls encounter Mera (comics) and Siren (DC Comics), the ocean-dwelling thieves, who prove to be a formidable match. In order to recover the stolen tome and return it to its rightful place, DC Super Hero Girls must band together and use their collective powers to successfully get back to land.