Reports are of a mystery thief who has robbed eight targets, and Spider-Man is suspected. At an aquarium museum, a man made of water strikes and robs a valuable artifact. When Spider-Man attempts to stop the robbery, he falls into eel-infested water but uses his web-cartridges to stop them, before fleeing.
While Peter is on a date with Mary Jane Watson, she gets a phone call from Morrie Bench, who tells her to meet up with him, and although she initially angrily refuses she heads off, telling Peter not to follow her. However, he follows her as Spider-Man. They meet up in a hotel lobby, where Mary Jane tells Morrie that she does not want to be with him, before leaving. Morrie uses his water powers to catch up with her, and at a water fountain he shows her what he is capable of doing as Hydro-Man. Spider-Man shows himself and attacks Hydro-Man, but the latter is able to overpower him. As Mary Jane continues to reject him, Hydro-Man loses his temper and creates floods of water. He and Spider-Man fight, and Hydro-Man nearly drowns him in a vat of water but Spider-Man escapes and saves Mary Jane before Hydro-Man can get to her.
After Mary Jane explains how she used to date Morrie to Spider-Man, she leaves in a taxi. Peter then creates some special web-shooters to counter Hydro-Man's water abilities. At home, Mary Jane is kidnapped by Hydro-Man who comes through her kitchen tap, and she wakes up in his hideout, where he shows her all of his treasure, making her realize he is the thief in the news. When she refuses to be with him again, he threatens to flood the city and kill everyone but them. As Hydro-Man begins to lose his temper again, Spider-Man arrives and uses his new webbing to immobilize him, although he is able to reform himself and start fighting Spider-Man.
As Hydro-Man and Spider-Man continue to fight, Hydro-Man gains the upper hand, but Mary Jane lures him to the top of the building, where Hydro-Man is far away from any source of water. In his anger, he leaps at Spider-Man but hits the floor, causing him to disintegrate into a puddle of water, before evaporating.
Later, Peter takes Mary Jane to the fair on a date.