
In the film, Neville is a solitary Army scientist, living in isolation as he tirelessly works on a vaccine for a virus transforming humans into vampire-like creatures known as Darkseekers. He conducts experiments on a female subject. When his dog, Sam, gets bitten and infected, Neville tries to save him using a serum he developed, but unfortunately fails and is forced to euthanize him. This tragic event pushes Neville out of his seclusion, leading him to encounter two other survivors who are headed towards a refuge for humans. Neville eventually figures out how to make his treatment effective, but his sanctuary is overrun by Darkseekers, causing him to leave behind a vial containing the blood of the cured woman with the survivors before he makes the ultimate sacrifice to protect the cure. The movie concludes with Anna and Ethan, the two survivors, reaching the camp and transferring the life-saving cure to them, while a voiceover shares that Neville’s actions saved mankind and his memory became legendary.