Ryan Walker returns to bay city victorious. Harper and his monsters have been defeated and the team is easing into their new school... when old enemies and dangerous new threats begin to complicate their lives. As Ryan tries to unravel the secrets of his birth parents, more questions arise: How are the monsters getting sentient and can anyone stop the human/monster hybrids that are stalking Bay City? As a mysterious new enemy weaves terrifying plans, both Ryan and MECH-X4 must level up so the team can unite and save the world.