April O'Neil, portrayed by Megan Fox, is an ambitious reporter working for Channel 6 news in the bustling city of New York. Her investigative journey leads her to uncover a notorious gang known as the Foot Clan, which has been wreaking havoc across the city. In her quest for the truth, she bravely interviews a dock worker regarding stolen chemicals often associated with genetic research, and these chemicals seem to be linked to the Foot Clan's sinister activities. As night falls, she ventures back to the docks and becomes an eyewitness to the Foot Clan unloading suspicious cargo. Armed with her smartphone, she attempts to capture footage of this crime in progress, but before she can do so, a shadowy figure appears and effortlessly takes down the Foot Soldiers one by one.
Having shared her harrowing experience with her coworkers and her skeptical boss, Bernadette Thompson, April finds herself dismissed and disbelieved. Meanwhile, the city of New York, alarmed by the increasing chaos instigated by the Foot Clan, strikes a lucrative deal with Eric Sacks—a powerful figure from Sacks Industries—to provide advanced security measures for law enforcement. Sacks reveals a personal vendetta against the Foot Clan, detailing how they once attacked his lab, resulting in the tragic loss of many top scientists, including April's own father.
The situation escalates as the Foot Clan's leader, the ruthless Shredder, becomes aware of the vigilante's interference and orders his minions to intensify their terror campaign in a bid to flush out this mysterious hero. The Foot Clan stages a dramatic attack on a subway station, taking hostages to draw the vigilante out into the open. Eager to uncover the truth, April rushes to the scene, only to find herself caught in a perilous hostage situation orchestrated by the Foot Clan. However, just when things seem dire, four incredible figures emerge and skillfully defeat the Foot Soldiers. April's curiosity is piqued when she pursues these mysterious vigilantes to a rooftop, capturing a photograph that reveals them to be none other than the humanoid mutant turtles—Leonardo, Michelangelo, Donatello, and Raphael, played by Pete Ploszek, Noel Fisher, Jeremy Howard, and Alan Ritchson respectively. The turtles demand she hand over the camera, but she faints at the sight of them. Upon regaining consciousness, she finds that the turtles have deleted her photo but their names resonate with her memories.
As the turtles return to their lair in the sewers, they face a stern reprimand from their master, Splinter, voiced by Tony Shalhoub. After being scolded for venturing into the city, the turtles find themselves in a tough position, which they call the "Hashi"—a spot where they must endure discomfort until they reveal their secrets. Meanwhile, April delves into a box of old documents and videos tied to a project called "Project Renaissance," led by her now-deceased father, Dr. O'Neil. She pieces together that the turtles she once cared for in her father's laboratory years ago have transformed into the incredible Ninja Turtles. Realizing the turtles’ origins, April races to convince her boss, Bernadette, of the truth, only to be met with disbelief and ultimately fired for her insistence on the turtles’ existence.
Frustrated, she turns to her cameraman, Vern Fenwick, played by Will Arnett, seeking his support. However, even he is skeptical, despite agreeing to visit her father's former lab partner, Eric Sacks. When April shows Sacks the photograph of the turtles, he explains the origins of Project Renaissance, elucidating how their experimentation with a mutagen led to the turtles’ transformation after a lab disaster. This mutagen, Sacks reveals, is the last known source, making it incredibly valuable.
The turtles, meanwhile, face their own challenges in the sewers as they endure the consequences of their nocturnal adventures in the "Hashi." When Splinter learns April is in danger because of her contact with them, he orders the turtles to find her. They blindfold April to protect their lair's location before bringing her to Splinter, who expresses gratitude, revealing how she saved their lives long ago. However, unbeknownst to her, Sacks has a hidden agenda and is in league with the Shredder, who has wicked plans to unleash a deadly virus upon New York.
As chaos unfolds, the Foot Clan attacks again, leading to an intense battle where Shredder captures Leonardo, Donatello, and Michelangelo, leaving Splinter gravely injured. Raphael and April are left to formulate a plan to rescue their friends. In a thrilling sequence, they reach Sacks's laboratory, where April bravely frees the captured turtles, and together they confront Shredder. After a fierce showdown, Shredder makes his escape. However, April, the turtles, and Vern flee down a snowy mountain with the Foot Clan hot on their heels.
With a strategic plan in mind, the turtles aim to confront Shredder atop Sacks's building before he can unleash his toxin upon the city. Meanwhile, April and Vern search for the mutagen inside the building, where Sacks reveals his dark truths, culminating in a confrontation where he admits to killing April’s father. In a heroic moment, Vern intervenes, knocking Sacks out, allowing April to recover the mutagen and join the turtles on the rooftop.
Unleashing the power of teamwork, they finally defeat Shredder, who, in the process, grows monstrous after coming into contact with spilled mutagen. The night closes with a light-hearted moment as Vern tries to impress April with a police vehicle, but the turtles, in a whirlwind of comedic chaos, steal the scene by destroying it while joyfully serenading her with a rendition of "Happy Together," encapsulating the bizarre yet heartwarming adventure they all shared.
