Robert Neville (Will Smith) is a brilliant scientist, but even he could not contain the terrible virus that was unstoppable, incurable, and man-made. Somehow immune, Neville is now the last human survivor in what is left of New York City and maybe the world. For three years, Neville has faithfully sent out daily radio messages, desperate to find any other survivors who might be out there. But he is not alone. Mutant victims of the plague - The Infected - lurk in the shadows... watching Neville's every move... waiting for him to make a fatal mistake. Perhaps mankind's last, best hope, Neville is driven by only one remaining mission: to find a way to reverse the effects of the virus using his own immune blood. But he knows he is outnumbered... and quickly running out of time.
Every day Neville prepares for nightly sieges from a
vampire horde. Neville spends the daylight hours repairing his house: boarding windows, hanging
garlic garlands, disposing of vampire corpses and gathering supplies. Once darkness falls, the infected come out of hiding and lay siege to Neville's house. They taunt him and attempt to entice him out he recognizes one vampire as a former friend, Ben Cortman.
After bouts of
depression and heavy drinking, Neville decides to find the cause of the disease. He obtains books and other research materials from a library, and through painstaking research he discovers the root of the vampiric disease: a strain of
bacteria capable of infecting both deceased and living hosts. However, he does not realize that the living hosts (the infected) are still inherently human, even though they exhibit all the signs of vampirism.
Neville comes across the seemingly uninfected woman, Ruth, abroad in the daylight and captures her. After the initial shock of seeing another human wears off, Neville becomes suspicious of Ruth and is skeptical of her story. He also notices that she is strongly against the killing of the vampires he feels that if her story of survival was true, she would have become hardened to their fate, nevertheless the two live in a wary state of tolerance. Eventually the two grow closer and one night Neville finds Ruth about to leave. Suspicious, he questions her motives, but ends up relating all of the trauma of his past to Ruth, who attempts to comfort him and the two make love. Afterwards Ruth agrees to let him take a blood test on her the following morning, she knocks him out just as he realizes she is infected. When he wakes up, Neville discovers a note left by Ruth. In it, she tells him that the infected have slowly been able to adapt to their disease to the point where they can spend short periods of time in sunlight and they are even attempting to rebuild society. They fear and hate Neville since he has unwittingly destroyed some of their people along with true vampires (dead bodies animated by the 'germ') during his daytime excursions and view him as a predator. In their quest to capture him, the infected sent one of their own to Neville.
Neville meets Ruth again in his prison; she informs him that she is a ranking member of this new society but unlike the others she doesn't fear and hate him. She tells him she had come to his prison to try and help him escape but that is now impossible. She acknowledges the need for Neville's execution, and slips him pills, claiming they will "make it easier." Emotionally broken, Neville finally accepts his fate and tearfully asks Ruth not to let this society get too brutal and heartless. Ruth kisses him and leaves.
Neville goes to his prison window and gets a glimpse of all the infected milling around in the yard waiting for his execution. When they spot him, he sees the fear, awe and horror in their eyes and he understands to them he is a scourge, just as they were a scourge to him at the beginning of the novel. Previously Neville saw the destruction of the infected survivors as a right and a moral imperative to be pursued for his own and mankind's survival, but now he finally acknowledges defeat. He is the only known immune human left in the world, the only survivor of the "old race".
He glimpses a future society where infection is normal and he, Neville, is a murderous biological deviant. As he turns away and swallows the pills, Neville grasps the reversal that has taken place and that just as vampires were legend in pre-infection times now he, an obsolete exemplar of old humanity, is legend in the eyes of the new race born of the infection. The sheer ridiculousness of it all causes Neville to chuckle as he dies, his last thoughts being " I am a new
superstition entering the unassailable fortress of forever. I am legend."
