The next night, the infected attack the house and overrun its defenses. Neville, Anna, and Ethan retreat into the basement laboratory, sealing themselves in with the woman Neville is treating. Discovering that the last treatment has turned out to be successful, Neville draws a vial of the cured woman's blood and gives it to Anna. He remembers his daughter Marley's repeated words "Look at the butterfly" as he notices a butterfly tattoo on Anna's neck. Neville pushes Anna and Ethan into an old coal chute, then sacrifices himself, using a hand grenade to kill the attacking infected.
Anna and Ethan escape to Vermont and locate the survivors' colony, where Anna hands over the cure. In the closing voice-over, she states that Neville's cure enabled humanity to survive and rebuild, establishing his legend.