[edit] Plot

Peter Parker, Harry Osborn, Mary Jane Watson visit a genetics laboratory at Columbia University with their high school class. While taking photos in the laboratory, Peter is bitten on the hand by a genetically engineered "super spider." Feeling unwell, he passes out shortly after his arrival home.
The next morning, Peter wakes to find that his vision is now naturally clear and that he has physically metamorphosed to become more muscular. At school later, he emits web strings from his wrists and has quick-enough reflexes to avoid being injured in a fight with bully Flash Thompson. As Peter infers that the spider's bite has given him spider-like abilities, he escapes school for buildings elsewhere, where he develops his new skills, quickly learning to scale walls, to jump long between building rooftops, and to swing via web.
Meanwhile, scientist and owner of Oscorp Norman Osborn, Harry's father, is attempting to preserve his company's military contract, knowing that losing it will bankrupt his business. He experiments on himself with his company's new, but possibly unstable performance-enhancing chemical vapor. The performance-enhancer increases his speed, strength, and stamina. The vapor having also made him insane, he easily murders his assistant, Mendel Stromm. A few days later, Norman kills several scientists (among them General Slocum) who threaten to drive Norman out of business.
Thumbing through the local classifieds, Peter sees a wrestling-tournament ad offering $3,000 to any participant who survives in the ring for three minutes. Figuring the purse to be enough for a car that will impress Mary Jane, Peter enters the tournament, unbeknownst to his aunt and uncle. Driving him on tournament day, Uncle Ben expresses concern for Peter, advising, "With great power comes great responsibility." Peter lashes out in frustration and leaves.
For the fight, Peter has chosen the name the Human Spider, but the ring announcer doesn't like it, opting to announce him as "Spider-Man," instead. Peter defeats his opponent, Bonesaw McGraw, but the man in charge only gives him $100 in prize money, using the excuse that he won in two minutes despite the ad's explicit claim of "three" minutes. When Peter turns around to go, a thief comes into the office, but Peter, in retaliation for the promoter's deception, does nothing to stop the burglar from escaping with the promoter's gate money. Not long after, Peter finds his uncle on the sidewalk, shot by a carjacker; he holds his uncle's hand as he dies in Peter's arms. Peter tracks down the carjacker, only to find that it's the same thief he earlier allowed to escape. The murderer then threatens to shoot Peter, but he breaks his wrist before he can pull the trigger, then the murderer falls out a window to his death.
Upon graduating from high school, Peter decides to use his abilities to fight injustice. He dons both a new costume and a new persona: Spider-Man. When he arrives in newspaper editor J. Jonah Jameson's office with the only clear images of Spider-Man, he is hired as a freelance photographer.
Norman, upon finding out that Oscorp's board members plan to sell the company, attacks and murders them at the World Unity Fair, but Spider-Man arrives to drive him off before he can do any more harm. Jameson quickly dubs Norman's persona the "Green Goblin". The Goblin later kidnaps Spider-Man to offer him a place at his side, but Spider-Man refuses, knowing that it is the right thing to do. At the Osborns and Parkers' Thanksgiving dinner, Norman figures out, unbeknownst to Peter, Spider-Man's true identity; that night, the Green Goblin attacks Aunt May.
As Aunt May recovers in the hospital, Mary Jane admits to Peter a crush on Spider-Man, her frequent rescuer. She inquires whether Spider-Man ever asks about her; Peter reflects on his own feelings, at which point Harry enters. Feeling betrayed by both his girlfriend and his best friend, Harry tells his father of whom Peter loves the most, unknowingly revealing to the Green Goblin Spider-Man's biggest weakness.
The Goblin takes Mary Jane and a Roosevelt Island Tramway car full of children hostage on the Queensboro Bridge, and Spider-Man arrives, just as Goblin has planned. The Goblin forces him to choose whom to save, dropping both Mary Jane and the tramway car simultaneously, but Spider-Man manages to save them all. The two fight for a bit, but the Goblin overpowers Spider-Man and throws him into the abandoned Smallpox Hospital on Roosevelt Island.
Peter, now heavily injured and his mask being burned to half, is brutally beaten up by the Goblin. The Goblin boasts of how he will later kill Mary Jane, but the tables turn as an enraged Spider-Man dominates him and forces him to unmask. As Norman contritely begs for forgiveness, his alter-ego slyly, via remote control, positions his glider to impale Spider-Man. He tells Peter that he had been a father to him and begs him to be a son to him. However Peter says that Ben Parker was his father. The Goblin yells Godspeed Spider-Man! and his glider rushes towards Peter to impale him. The superhero avoids the attack, leading the glider to impale Norman instead. Norman uses his last breath to state merely, "Peter, don't tell Harry."
Spider-Man brings a now dead Norman to the latter's apartment. Just as he has laid the body down, Harry arrives, stunned and angered, but the darkness prevents Peter's reveal. Harry turns to pull a gun from a drawer, but Spider-Man is already gone by the time he has turned back.
Upon the conclusion of Norman’s funeral, before leaving, Harry vows to Peter that he will kill Spider-Man as vengeance for his own father's death; Peter is all he has left now, he says. Mary Jane confesses her love to Peter and kisses him, but Peter hides his true feelings, feeling that he must protect her from Spider-Man's enemies' attention. Walking away from a now distraught MJ, he recalls Uncle Ben's famous words, "With great power comes great responsibility," and accepts his new life as Spider-Man.