Denny Colt (Gabriel Macht), also known as "the Spirit", learns about a major case from Detective Sussman (Dan Gerrity) involving his nemesis, "the Octopus" (Samuel L. Jackson). The Spirit dons his costume and travels across rooftops, saving a woman before connecting with Officer Liebowitz (Frank Miller). At the swampland,femme fataleSand Saref (Eva Mendes) rises from the water to shoot Sussman.
The Spirit and Liebowitz find the wounded Sussman. Sand and her husband Mahmoud (Eric Balfour) had earlier fled with chests they recovered from the water. Shot at, Sand escaped, leaving one chest behind which was retrieved by Octopus. The Octopus kills Liebowitz, and his cloned henchmen attack the Spirit. His accompliceSilken Floss(Scarlett Johansson) flees with the chest as the two arch-nemeses fight.
The next morning, the Spirit is awakened by his lover,Dr. Ellen Dolan(Sarah Paulson), daughter of Commissioner Eustace Dolan (Dan Lauria). He is undeterred by his gunshot wounds. He notices a gold locket in Sussman's hand, which had been torn from Sand Saref's neck. The locket contains pictures of a much-younger Colt and Sand, and had been his gift to her. Sand had become disenchanted with the city's corruption following the death of her father, a police officer, and left for fifteen years. In a secret lair, the Octopus and Silken Floss discover their chest contains theGolden Fleece, not the Blood of Heracles, as expected. Sand and Mahmoud visit an underworld figure who sold them the location of the treasure, and it is implied he gave the location to the Octopus.
Having fully regenerated, Commissioner Dolan calls The Spirit away to a case and relates Sand's history as one of the world's great jewel thieves. While arresting her, he reveals he knows she is looking for the Golden Fleece, and she shoves him through a window, which he survives. The Spirit receives a tip on the location of the Octopus's lair but is captured while investigating. The Octopus reveals that his and Floss's experimentation led to the creation of an immortality serum. The Octopus first tested it on Colt's dead body; Colt came back to life and earned the ire ofDeathfor escaping her clutches. Eventually, the Octopus injected himself with the serum, but he needs the blood ofHeracles, a demi-god, to perfect the formula. The Spirit escapes by seducing assassin Plaster of Paris (Paz Vega), who as a parting gift turns on The Octopus. When the Spirit mentions Sand's name, she stabs him out of spite.
After recovering, the Spirit stumbles to the city docks and collapses into the water, where the Lorelei (Jaime King), the Angel of Death, confronts him. He initially submits but changes his mind after remembering the women he has known. As he swims to the surface, she vows to have him. At the projects, Sand, Floss, and their henchmen meet to exchange the Blood of Heracles for the Golden Fleece. Sand attempts to convince Floss to leave the Octopus before he kills her. Floss gains the upper hand and the Octopus asks Floss for the vase of blood. As the Spirit suddenly materializes, Floss drives off, unable to take a side.
The Octopus shoots a series of progressively larger guns at the Spirit, apparently killing him, but Dolan'sSWATteam storms the area and opens fire. The Octopus is maimed; as he desperately tries to drink the Blood of Heracles, Sand shoots the vase. The Spirit rises, shown to be wearing a bullet-proof vest, and blows up the Octopus with a grenade while Sand uses the Golden Fleece to protect them from the explosion.
The Spirit gives Sand her locket back. They kiss as Ellen looks on, feeling betrayed. The old flames bid each other goodbye and the Spirit convinces Dolan to let Sand go in gratitude for saving him and the world. Nearby, Floss discovers one of the Octopus's severed fingers crawling towards her; she picks it up and departs with two of the clones. Meanwhile, the Spirit and Ellen make amends and embrace.