A young Peter Parker discovers his father Richard Parker’s study has been burgled. Gathering up hidden documents, Peter’s parents take him to the home of his Aunt May and Uncle Ben, then mysteriously depart.
Years later, a teenaged Peter attends Midtown Science High School, where he is bullied by Flash Thompson and has caught the eye of the beautiful Gwen Stacy. At home, Peter finds his father’s papers and learns he worked with fellow scientist Dr. Curt Connors at Oscorp. Sneaking into Oscorp, Peter enters a lab where a “biocable” is under development from genetically modified spiders, one of which bites him. On the subway ride home, he discovers that he has developed spider-like abilities, such as sharp senses, reflexes and speed.
After studying Richard’s papers, Peter visits the one-armed Connors, reveals he is Richard Parker’s son and gives Connors his father’s “decay rate algorithm”, the missing piece in Connors’ experiments on regenerating limbs. Connors is being pressed by his superior, Dr. Ratha, to devise a cure for the dying (but unseen) head of Oscorp, Norman Osborn. In school, Peter gets into trouble after a basketball challenge with Flash in which Peter accidentally shatters the backboard glass. His uncle changes work shifts to meet with the principal and asks Peter to replace him walking home with May that night. Peter gets distracted and helps Connors regenerate the limb of a laboratory mouse. Peter’s failure causes an argument with Ben and he leaves. At a nearby deli, a cashier refuses to let Peter buy milk when Peter is two cents short; when a thief suddenly raids the store, Peter indifferently observes. While searching for Peter, Ben attempts to stop the thief and is killed. The thief escapes as Peter finds Ben dead on the sidewalk.
Afterward, Peter uses his new abilities to hunt criminals matching the killer’s description. After a fall lands him inside an abandoned gym, a luchador-wrestling poster inspires him to create a mask to hide his identity. He adds a spandex suit and builds mechanical devices to attach to his wrists to shoot a biocable “web”. Peter accepts a dinner invitation from Gwen, where he meets and has a tense conversation with her father, police captain George Stacy, over the new masked vigilante’s motives. After dinner, Peter reveals his identity to Gwen and they kiss.