Seymour Gutz has become the Mutagen Man again, and he's randomly mutating New Yorkers all over the city! In fact, he's even mutated Michelangelo! (Did you know you could further mutate a mutant? The Teenage Mutant Ninja Turtles sure didn't!) The Turtles need to get Seymour back to TCRI to formulate a cure, but first they need to rescue him from the Shredder, who has captured him with the desire for the Mutagen Man to create an army of mutants!