Following the Battle of New York, Adrian Toomes, portrayed by Michael Keaton, finds himself in a precarious situation as his salvage company is unexpectedly stripped of its contract by the Department of Damage Control (D.O.D.C.). This governmental body, overseen by Anne Marie Hoag (Tyne Daly) in partnership with Tony Stark (Robert Downey Jr.), renders Toomes' business efforts futile. Having invested a significant amount of money into his operations, Toomes is furious at the loss and coerces his employees into keeping the advanced Chitauri technology they previously recovered. He resolves to use this cutting-edge tech to manufacture and sell illegal weapons.
Fast forward eight years, Toomes operates a prosperous underground weapons business built upon that alien technology, complete with a specialized flying suit that allows him to gather even more alien materials. Meanwhile, Peter Parker, played by Tom Holland, is eager to prove himself to Stark after being briefly enlisted into the Avengers. As he awaits an invitation to join the superhero team, Peter juggles the challenges of high school at the Midtown School of Science and Technology, with his Aunt May (Marisa Tomei) and head of security Happy Hogan (Jon Favreau) keeping a watchful eye on him.
Parker chooses to step down from the academic decathlon team to focus on his superhero pursuits and has developed a crush on Liz, a fellow team member. As Parker tries to maintain his double life, he inadvertently reveals his true identity to his best friend Ned (Jacob Batalon). Following an encounter with criminals armed with Toomes' advanced weapons, Parker attempts to inform Happy about these dangers, only to be dismissed as overreacting.
On a fateful night, Peter discovers that Toomes’ associates, including Jackson Brice (Logan Marshall-Green) and Herman Schultz (Bokeem Woodbine), are dealing weapons to local crime lord Aaron Davis, played by Donald Glover. After a chaotic showdown where Parker is almost drowned by Toomes, he learns a hard lesson about the responsibility that comes with his powers.
Facing continuous setbacks, Parker tries to thwart Toomes’ operations, which culminates in a disastrous event where a D.O.D.C. truck he attempts to protect ends up compromising Peter’s school life – particularly the highly-anticipated national tournament. The stakes only rise when the power core that he inadvertently brings along turns out to be a volatile Chitauri grenade, leading to a frantic rescue of his friends from a precarious elevator situation.
Determined to impress Stark and further his role as Spider-Man, Peter tracks down Toomes, hoping to stop an arms deal aboard the Staten Island Ferry. However, after failing to capture Toomes, Peter faces unforeseen consequences that lead to Stark stripping him of his suit, pushing him back into the reality of being a regular high schooler.
As fate would have it, Parker discovers that Liz is, in fact, Toomes' daughter, and upon risking everything to save her, he uncovers Toomes' plan to hijack a D.O.D.C. plane carrying weapons. With a makeshift Spider-Man suit, Parker navigates perilous confrontations, ultimately leading to a deadly showdown with Toomes as the plane crashes on the Coney Island beach.
In a gripping climax, Parker's moral compass shines through when he chooses to save Toomes over exacting revenge, ultimately leaving him for the authorities as a newly emerging hero. Despite his achievements, Parker turns down Stark's offer to join the Avengers permanently and returns to a semblance of normal life, all while preparing for the new challenges ahead, just as Aunt May catches him in his Spider-Man costume for the first time. In a twist before the credits roll, a fellow inmate, Mac Gargan (Michael Mando), confronts Toomes, hinting at a future filled with peril and intrigue.
