On their 15th birthday, the four mutant turtle brothers—Leonardo, Raphael, Donatello, and Michelangelo—are finally permitted by their mentor, Master Splinter, to leave their sewer home and explore the surface of New York City for the very first time. While adjusting to the dazzling but chaotic human world, they witness a teenage girl named April O'Neil and her scientist father being abducted by a secretive, brain-like alien race known as the Kraang. To rescue them, the brothers must quickly learn to move past their sibling rivalries, master their ninja teamwork, and weaponize their skills against advanced alien technology—an adventure that inadvertently alerts their ultimate nemesis, The Shredder, to their existence.