After the Battle of New York, Tony Stark (Robert Downey Jr.) creates the Department of Damage Control to clean up after superhuman battles, inadvertly forcing Adrian Toomes (Michael Keaton) and his salvage crew out of business. Toomes and his men then decide not to surrender the Chitauri technology they have already scavenged and use it to steal weapons and supply them to criminal enterprises.
Years later, after the Battle of Leipzig, Peter Parker (Tom Holland) is eager to join the Avengers, but is told by Stark that he's not yet ready. Peter is then forced to return to his old life as a student of Midtown Science and Technology School alongside his friends Ned (Jacob Batalon) and Michelle (Zendaya), his rival Flash Thompson (Tony Revolori) and his longtime crush Liz Allan (Laura Harrier). They're members of the school's academic declathon team, but Peter has recently quit to focus on his "internship" at Stark Industries, a cover for his crimefighting activities, despite Aunt May's (Marisa Tomei) objections.
Spider-Man confronts a group of criminals using Chitauri weapons to rob an ATM, but they escape and Ned accidentally finds out his secret identity. Spider-Man later finds Toomes' associates Herman Shultz (Booken Woodbine) and Jackson Brice (Logan Marshall-Green) selling weapons to gangster Aaron Davis (Donald Glover) and intervenes, but Shultz and Brice escape while Peter is nearly killed by the Vulture and rescued by Stark.
Determined to stop the Vulture, Peter and Ned retrieve a Chitauri weapon that Brice had left behind and remove its power core. A tracking device leads Shultz and Brice to Midtown, but Peter and Ned evade them and Peter plants a spider-tracer on Shultz that leads back to Virginia. Peter then rejoins the declathon team and accompanies them to Nationals in Washington, D.C., to follow his lead on Shultz. Peter and Ned disable Peter's suit's tracker and unlock its secret features, including an A.I. interface. Spider-Man then locates Toomes, Shultz and their tinkerer, Phineas Mason (Michael Chernus), intercepting a DDC truck to steal more weapons. Spider-Man confronts the Vulture, but is overpowered and trapped in the truck, missing Nationals and disappointing his friends.
Peter finds out that the Chitauri power core left with Ned is unstable and that his friends are in danger. He manages to escape from DDC's headquarters but is too late to prevent the core from exploding while the team is visiting the Washington Monument, leaving them trapped in a collapsing elevator. Spider-Man manages to climb to the top while evading the police and catch the elevator before it plummets, saving his classmates. Peter later invites Liz to the homecoming dance.
Returning to New York, Spider-Man locates Davis and persuades him to reveal the Vulture's whereabouts. Spider-Man then confronts the Vulture and his men at the Staten Island ferry and captures Brice, but the Vulture escapes by using one of the Chitauri weapons to tear the ferry apart. Iron Man arrives and saves the passengers, but reprimands Peter for his recklessness and takes his suit, forcing Peter to go back to the homemade version. Peter goes to pick up Liz and finds out that Toomes is her father. Toomes deduces that Peter is Spider-Man as well and threatens retaliation if he interferes in his plans again.
Peter realizes Toomes is planning to hijack a DDC plane transporting the Avengers' weaponry from Stark Tower to the team's new headquarters in upstate New York and is forced to leave Liz to stop him. He's ambushed by Shultz at the bus yard, but Shultz is then knocked out by Ned. Spider-Man confronts Toomes in his lair, where Toomes attempts to persuade Peter to his side, claiming that he created his operation to secure Liz's future. Spider-Man is resolute, so the Vulture destroys the building's support beams, trapping Spider-Man under the rubble. Spider-Man manages to wrest himself free and intercept the Vulture. The DDC plane is damaged, but Spider-Man manages to steer it towards an empty area near Coney Island, where he once again fights the Vulture. Toomes' suit is damaged in the process, trapping Toomes in a fire, but Peter rescues him and leaves him for the police.
Liz tells Peter that her mother and her are moving away due to Toomes' arrest and names Michelle as the new president of the declathon team, reveaing her full name as Michelle Jones, although her friends call her "MJ". Peter later visits Stark and declines his invitation to join the Avengers, having realized the importance of being a friendly neighborhood Spider-Man. Peter returns home to learn that Stark has made him a new suit and puts it on just as Aunt May walks in, and she finds out that Peter is Spider-Man.
In a mid-credits scene, Toomes is locked up in the Raft and approached by another convict, Mac Gargan (Michael Mando), who reveals that several criminals aprehended by Spider-Man are banding together to get revenge. Toomes, however, chooses not to expose Peter's secret identity.
In an after-credits scene, Captain America (Chris Evans) shoots another of several PSA videos that are shown to Midtown's students throughout the school year.
Michelle playfully teases Peter and is clearly harboring a crush on him, which he is oblivious to.
Ned is skilled with computers and defeats Shultz with Peter's webshooters in the bus yard.
Flash is the wealthiest kid in Midtown and resents Peter for often upstaging in in academics. Spider-Man "borrows" his car to pursue the Vulture and ends up wrecking it.
Betty is Liz's best friend and a school reporter.
Toomes is nicknamed "The Vulture" because he scavenges weapons like a Vulture.
Shultz wants to be called "Shocker" and displays interest in getting a suit of his own.
Brice isn't arrested. He's accidentally killed by Toomes with a Chitauri weapon after being kicked off the team for attracting Spider-Man's attention and threatening to go to the authorities.
Davis helps Spider-Man find Toomes because he doesn't want destructive Chitauri weapons in the neighborhood that his nephew lives in.
Stark Tower has been sold to an anonymous buyer and the DDC is moving its equipments to the Compound.
The DDC plane that the Vulture is targeting is transporting, among others, a new Vibranium shield, an Asgardian magic belt, the Hulkbuster, the Mark 42 and crates full of Arc Reactors.
Tony and Pepper are back together. Tony organizes a press conference to introduce Spider-Man as a member of the Avengers, and when Peter declines, he instead uses it to publically propose to Pepper.
Happy is appointed Peter's supervisor. Early on, Peter leaves him numerous "reports" of the petty crimes that he's stopped in hopes of attracting Stark's attention.
Gargan has a scorpion tattoo on his neck, a scar running down his face and surgical pins on his arm.
Stark offers Peter the Iron Spider suit as part of his membership in the Avengers, which Peter declines. The "new" suit he later finds is basically the hight-tech Stark suit stripped of all its tech.
Spoiler:
