“THE SEA BEASTS FROM ONE BILLION B.C.” John Cook steals Professor Richards’ experimental ray gun, which will turn any normal fish into a large sea monster! Now it’s up to Aquaman and Aqualad to find a way to get these creatures back to normal size!

Professor Richards created a machine which could both devolve and evolve sea creatures while placing them under control. John Cook steals it and uses it against Aquaman. Arthur and Garth have to face prehistoric forms of aquatic life, modern ones and versions from the future.