Peter Parker has begun to feel secure in his life and plans to propose to Mary Jane. While Peter and Mary Jane are on a date, a small meteorite crashes nearby, and an extraterrestrial symbiote attaches itself to Peter's moped. Meanwhile, escaped convict Flint Marko falls into a particle accelerator that fuses his body with the surrounding sand. The result allows him to shape shift at will, becoming the Sandman. Peter's best friend, Harry Osborn, who seeks vengeance for his father's death, which he believes Peter caused, attacks him. During the scuffle, Harry injures his head and suffers from partial amnesia, making him forget his vendetta.
Later, during a festival honoring Spider-Man for saving Gwen Stacy's life, Sandman attempts to rob an armored car, and overpowers Spider-Man. Gwen's father, police officer Captain Stacy, later informs Peter and Aunt May that Marko is the one who killed Ben Parker. A vengeful Peter waits for Marko to strike again. The symbiote bonds with his costume while he is asleep; Peter discovers that not only has his costume changed, but his powers have been enhanced as well. Perhaps capitalizing on Peter's current conflicted and anguished state of mind, the black suit brings out the more vengeful, selfish and arrogant side of Peter's personality. Wearing the new suit, Peter locates Flint Marko, fights him in a cavernous underground subway tunnel and, upon discovering that water can dissolve Marko's body, rips open a large water pipe to deliver what he believes to be a lethal torrent of water.