Plot
In the year 2019, a global plague caused by an infected vampire bat has transformed most of the world's human population into immortal vampires. As the population of uninfected humans decreases, vampires are faced with a severe blood shortage, with those deprived of blood degenerating into bestial monsters called "subsiders". Because sunlight is deadly to vampires, the vampires are active during the night, and use underground passages and UV-filtered cars for daytime travel.
Humans are captured and kept alive for their blood while scientists search for a synthetic blood substitute. Edward Dalton is the head hematologist for Bromley Marks, the largest corporate supplier of human blood. With his colleague Christopher Caruso, they work to develop a blood substitute, which they test on soldiers in the vampiric national army. Powerful CEO Charles Bromley watches these tests eagerly, wanting to build a fortune by selling the synthetic substitute to most people, while secretly planning to keep pure human blood for himself and other wealthy vampires.
While driving home, Dalton accidentally runs another vehicle off the road. Discovering the occupants are humans, Dalton hides them from the police. Before they leave, their leader, Audrey, sees his Bromley Marks identification, thereby learning Edward's name and occupation. At home, Edward is surprised by his estranged brother Frankie with a gift of a bottle of pure human blood. The gift reignites a long-standing argument – Edward refuses to drink human blood, while Frankie, a soldier, enjoys it. A subsider invades the house, forcing the brothers to kill it together.
The next morning, Audrey visits Edward and sets up a meeting with Lionel 'Elvis' Cormac, a human who was cured of vampirism. Before Cormac can explain his reversion, a military team arrives with Frankie, who follows Edward and intends to capture Cormac and Audrey. Audrey knocks Frankie unconscious, and the three escape. Cormac reveals that he was cured of vampirism when a car crash ejected him from his sun-proof vehicle. Elvis burst into flames but fell into a river before the sunlight killed him. He theorizes that the brief exposure to sunlight turned him human. Edward agrees to help Cormac recreate the cure and prevent humans from being wiped out.
Edward meets Senator Wes Turner, a human sympathizer secretly helping to develop a cure. Vampire soldiers capture an approaching human convoy and track the vineyard's location, forcing Turner and the humans to flee. Audrey, Cormac, and Edward stay behind. After many painful trials, they successfully cure Edward of vampirism. They later find Turner and all the humans slaughtered and drained of blood.
Alison Bromley, one of the captured humans, is revealed to be the beloved daughter of Charles Bromley. As she refuses to become a vampire, Charles has Frankie forcibly turn her. However, she refuses to drink human blood and devolves into a subsider, and is executed by being dragged into sunlight. Upset by her death, Frankie seeks his brother. The military imposes martial law to curb the subsider population.
Edward, Cormac, and Audrey break into Christopher's home and ask him to help spread the cure. Having finally discovered a viable blood substitute, Christopher rejects the cure and calls in soldiers, who capture Audrey while Cormac and Edward escape. They are found by Frankie, who agrees to help, but instinctively bites and feeds on Cormac. As it turns out, a cured human is immune to vampire bites, while cured vampire blood is a cure in itself.
Trying to save Audrey, Edward surrenders himself to Charles. Edward taunts Charles into biting him, turning Charles human. Edward leaves Charles to be killed at the hands of blood-starved vampire troops. Frankie arrives and sacrifices himself to the soldiers, allowing Edward and Audrey to escape. In the ensuing feeding frenzy, only a few surviving soldiers are cured. To conceal the cure, Christopher kills the soldiers and is about to shoot Edward and Audrey when Cormac kills him. The three survivors drive off into the sunrise with the cure that will change the general population back to restore humanity.