The barrier preventing monsters from returning to the surface was broken. Yet a fail-safe was placed to ensure that the humans would never see them again. New creatures appear in a cave in the Everfree, and nopony is prepared for their new visitors.
The Rainbooms and the Turtles are back again, and in another dimension where another team of mutant turtles live. Join the teams as they learn to work together against allying threats from both universes.