Several months after Otto Octavius' sacrifice, Peter Parker plans to propose to Mary Jane Watson, who has just made her Broadway musical debut. A meteorite lands at Central Park, and an extraterrestrial symbiote follows Peter to his apartment by latching on to his motorbike after he and Mary Jane leave there after stargazing. Harry Osborn, seeking vengeance for his father's death and having taken the performance-enhancing gas, attacks Peter with his father's Green Goblin technology, but the battle ends in a stalemate with Harry crashing down and having partial amnesia, losing his memory of Peter as Spider-Man. Meanwhile, police pursue escaped convict Flint Marko, who visits his wife and sick daughter before fleeing again. Falling into an experimental particle accelerator that fuses his body with the surrounding sand, he transforms into the Sandman, who can control sand and reform his body with it.
During a festival honoring Spider-Man for saving Gwen Stacy's life, Peter kisses her, angering Mary Jane. Meanwhile, Marko robs an armored truck, easily defeats Peter and flees. NYPD Captain George Stacy, Gwen's father, informs Peter and his Aunt May that Marko was uncle Ben's true killer; the deceased Dennis Carradine was Marko's accomplice. At his apartment, while Peter sleeps in his Spider-Man suit to wait for Marko, the symbiote assimilates the suit; Peter later awakens at the top of a building, discovering that his costume has changed to black and his powers are enhanced; however, the symbiote brings out his dark side. Peter locates and battles Marko in a subway tunnel. Discovering that water is Marko's weakness, he opens a pipe, releasing water that reduces Marko to mud and washes him away.
Peter's changed personality alienates Mary Jane, who is struggling in her career because of her shows receiving negative reviews from critics. She shares a tender moment with Harry, but leaves afterward in regret. Harry recovers from his amnesia, urged by a hallucination of his father and coerces Mary Jane into breaking up with Peter. After Mary Jane tells Peter she loves "somebody else," Harry meets with Peter and claims to be that person. Peter confronts Harry over this and spitefully tells him that his father never loved him. Another battle ensues, with Harry throwing a pumpkin bomb at Peter, who deflects it back, disfiguring Harry's face.
At the Daily Bugle, Peter exposes rival photographer Eddie Brock, whose fake photos depict Spider-Man as a criminal. Publisher J. Jonah Jameson fires Brock and hires Peter to be a staff photographer. Later, Peter brings Gwen to a jazz club, where Mary Jane now works. Peter passionately dances with Gwen in front of Mary Jane, in order to make her jealous. Gwen, realizing this, apologizes to Mary Jane and leaves. After assaulting the bouncers and accidentally hitting Mary Jane, Peter finally realizes that the symbiote is corrupting him. Retreating to a church's bell tower, upon realizing high-pitched sounds weakens the creature, Peter removes the symbiote, where it bonds with Brock, transforming him into Venom. Brock locates Marko, who survived being washed away, and convinces him to join forces to defeat Peter.
Brock abducts Mary Jane and holds her captive from a web high at a construction site, while Marko keeps the police at bay. After Harry refuses to help Peter, he finally learns the truth about his father's death from his butler. While Peter battles Brock and Marko, Harry arrives to help him with his Green Goblin technology and saves Mary Jane. Brock attempts to impale Peter with Harry's glider, but Harry jumps in and is impaled himself. Peter, remembering the symbiote's weakness, assembles a perimeter of metal pipes to create a sonic attack, weakening it and allowing Peter to separate Brock from the symbiote. He activates a pumpkin bomb from Harry's glider and throws it at the symbiote. However, Brock, who became addicted to its influence, attempts to save it, and ends up vaporized along with the symbiote.
Afterward, Marko explains that Ben's death was an accident that has haunted Marko ever since; Peter forgives Marko, allowing him to escape. Harry and Peter reconcile before Harry subsequently dies from his injuries. Sometime later after Harry's funeral, Peter and Mary Jane reconcile and share a dance at the jazz club.
Tobey Maguire as Peter Parker / Spider-Man:
Kirsten Dunst as Mary Jane Watson:
James Franco as Harry Osborn / New Goblin:
Thomas Haden Church as Flint Marko / Sandman:
Topher Grace as Eddie Brock / Venom:
Bryce Dallas Howard as Gwen Stacy:
James Cromwell as Captain George Stacy:
Rosemary Harris as May Parker:
J. K. Simmons as J. Jonah Jameson:
based on the Marvel Comics character Spider-Man.
the final installment in Raimi's Spider-Man trilogy.