Years ago, Hamato Yoshi, a Japanese ninja master, moves to New York City and purchases four baby turtles, before witnessing a shady deal in an alleyway; in the resulting fight, he and the turtles are coated by a strange chemical mutagen, transforming Yoshi into a humanoid rat and the Turtles into anthropomorphic form. In the present, Yoshi, now known as Splinter, has trained the Turtles-Leonardo, Donatello, Michelangelo and Raphael-in the art of ninjutsu, and celebrates their fifteenth "Mutation Day" with them. Splinter begrudgingly allows the Turtles to visit the surface world, where they encounter pizza for the first time and observe a teenager named April O'Neil, with whom Donatello becomes infatuated. April and her father Kirby are then attacked by a group of strange men, and, unable to work together, the Turtles fail to stop them from being kidnapped-immediately after, Michelangelo discovers that the kidnappers are androids piloted by brain-like aliens, but the other Turtles dismiss him. Splinter chastises the Turtles for their failure, yet agrees that they have to take action, deeming Leonardo the Turtles' leader in order to help them function as a team. The Turtles track down the kidnappers' van and their associate, Snake. In the process, they discover another canister of the chemical mutagen.