Martin, a drifting loner, arrives in a quiet town with a singular purpose: to find a woman named Ana. A teen named Peter directs him to a cemetery where Ana lies buried, and as Martin mourns and reflects on their shared past, danger quickly closes in. A trio of thugs led by Caleb track him down, threatening to kill him right there. Martin tests their resolve, hoping they’ll back off, but the situation spirals when Peter intervenes and tries to halt the assault. In the struggle, Caleb fatally stabs Martin and the group leaves him for dead in a ditch.
Peter flags down Lieutenant De Luca, who turns out to be Caleb’s father. The two confront Caleb, who claims it was self-defense. De Luca, convinced of a cover-up, brands Caleb a liar and orders him to bury the truth. Peter witnesses the entire exchange before De Luca departs. When the coast is clear, Peter discovers that Martin is still alive and brings him back to his home.
Peter persuades his wary mother, Monica, to help, though Martin flatly refuses first aid, insisting that his blood is contagious. Through their conversation, Martin learns Ana’s fate: she killed herself after giving birth. Then Martin vanishes. De Luca returns later to bury Martin’s body, only to find it gone and immediately suspects Peter. He sends Caleb to handle whatever remains, but Caleb beats Peter for his stubborn insistence that he knows nothing of Martin.
Martin returns in a dramatic turn, killing Caleb’s friends and setting Caleb on fire. De Luca interrogates Peter again, and the boy admits he moved Martin’s body. De Luca, initially skeptical that Martin could have survived such injuries, nevertheless identifies the reappearing man as his son’s aggressor and a city-wide manhunt begins.
After a drunken binge, De Luca tracks down Peter again and drags him to a secluded place for another round of questioning. When Peter stays tight-lipped, De Luca torches him. Martin intervenes, knocks De Luca unconscious, and rescues Peter, taking him back to Monica’s house. As Monica calls for help, Martin recites a Latin blessing and rubs Peter with his own blood, a moment that seals Peter’s fate in unexpected fashion.
At the hospital, Peter mysteriously recovers and is released. The two flee the town, but the police catch up with Martin, and De Luca forces a confrontation aboard a bus. He abducts Monica and Peter and coerces them to reveal how Peter survived. In a brutal turn, he makes Monica, a nurse, perform a transfusion from Martin to Caleb. Martin pleads with her not to do it, insisting that his blood must be blessed to keep infection at bay, but De Luca ignores him.
Caleb is momentarily healed by Martin’s blood, yet the infection takes hold and Monica dies. The police converge on De Luca’s home, but he refuses to come out, and the siege continues. Peter goes to the jail to free Martin, only to discover that Martin cannot revive the dead. Still, Martin pushes them to stop Caleb. When Martin reaches De Luca’s house, he finds the two men missing and a slain police force, save for the chief. Martin kills the wounded chief, revealing that he, too, is infected. They pursue Caleb and De Luca, and a dramatic car collision leaves Peter wounded and accidentally infected by Martin’s blood. Martin ties Peter to a tree and leaves him behind as De Luca’s fate is sealed with his own death.
A passing motorist with a pet dog frees Peter from his bonds. Martin closes in on Caleb, who has already killed and fed on a young girl. Peter arrives, his face torn and smeared from feeding, and drags Caleb into the daylight, protected by thick clothing. The sun proves fatal for Caleb, who disintegrates before their eyes.
In a final, quiet reveal, Martin tells Peter that he and Ana are Peter’s true parents, and that Monica only adopted him after Ana’s suicide. Martin urges Peter to be stronger than his adoptive mother and asks him to let him die in the sun. As Peter walks away, a chilling detail surfaces: he had fed on the motorist’s pet dog earlier, and now drives off with a darker, changed resolve.
