The camera glides over the bustling streets of New York City, capturing the attention of news reporter April O'Neil as she delves into a puzzling series of organized thefts plaguing the city. In a montage of shadows and quick movements, we see members of the Foot Clan stealthily pilfering items from unsuspecting citizens, leaving behind no traces of their criminal exploits. After a long day, April wanders into a deserted lot, where she encounters a group of thieves in the act of robbing a van. Just as they overpower her, the lone light at the lot flickers out. By the time the police arrive, the thugs find themselves bound, and curiosity piques as April discovers a sai on the ground, tucking it away in her purse, oblivious to the mysterious pair of eyes peering from a manhole's lid—someone cursing under his breath before vanishing into the shadows below.
In the murky depths of the sewer, a unique figure introduces the story as it transitions to four humanoid turtles adorned in colored eye-bands, celebrating their latest adventures. They return home to their mentor, Splinter, a wise rat who questions whether they were seen during their escapades and imparts crucial lessons on the essence of ninja training—a lesson interrupted by one turtle's pizza craving. Amidst the chaos, Raphael (Josh Pais), visibly upset about losing his sai, dons a trench coat and hat and heads out to watch a movie. Meanwhile, the other turtles, Donatello (Corey Feldman) and Michelangelo (Robbie Rist), anticipate the arrival of their pizza, cheekily saving a few bucks off the late delivery.
As Raphael strolls through the city, he stumbles upon a couple of thugs harassing an old woman. Chasing the criminals into a nearby park, he confronts Casey Jones, a vigilante clad in a hockey mask wielding a baseball bat. Their spat turns into a scuffle, leaving Raphael fuming after being dubbed a "freak." Later, he returns home, where Splinter calms him down with sage advice.
The following day, April visits the police chief, Chief Sterns, who admonishes her for meddling in the city’s crime issues. On her way home via the subway, she encounters a group of masked thieves, led by one of the Foot Clan, who assaults her. Just as she tries to retaliate, Raphael intervenes, disguised in a hood. He heroically rescues April, but their hideout is soon invaded by the Foot Clan, forcing them to flee.
In a flashback, Splinter explains the origins of the turtles—mutated by toxic waste, they were taken in by him, and he trained them in ninjutsu. Each turtle has his own weapon: Raphael wields two sais, Leonardo (Brian Tochi) prefers his twin ninjato, Donatello carries a bo staff, and Michelangelo enjoys using nunchaku.
As they bond over pizza in April's apartment, a perilous discovery awaits upon their return home—Splinter has vanished. With nowhere to turn, the turtles take refuge in April's place. Meanwhile, Danny, a young pickpocket, grapples with his own dilemmas while seeking solace in his father's expectations. He inadvertently leads the Foot Clan to their hideout, revealing a clash of destinies.
Amidst chaos, the turtles regroup and prepare for battle against Shredder, the nefarious leader of the Foot Clan. A pulsating climax unfolds on the rooftops of New York, with an epic showdown between the turtles and Shredder, who relishes in mocking their struggle. In a moment of desperation, Splinter reveals himself, surprising Shredder and forcing him to contend with his past.
With thrilling moments of martial artistry, friendship, and the fight for justice, the turtles ultimately overcome, reuniting with their beloved mentor Splinter as the police move to apprehend the remaining criminals. Just before the film draws to a close, April delivers the compelling news story, capturing the turtles' antics and their victory with a heartfelt gratitude headed towards Raphael, and they all share in a joyful rallying cry of "cowabunga," culminating in a celebration of camaraderie and laughter as the curtain falls.
