Claire Porter, Stephanie Lemelin, lies in a hospital bed as French police led by Captain Klaus Pistor, Sebastian Roché, question her after a brutal attack that leaves her husband Henry Porter, Brian D. Johnson, and their son Peter Porter, Oaklee Pendergast, dead. The motive remains murky until Claire describes a shadowy figure that resembled a man, prompting the arrest of the brutish local man Talan Gwynek, Brian Scott O'Connor, for the murders. Claire dies later in the hospital, a grim turn that deepens the mystery.
An expatriate attorney, Katherine Samantha Moore, A. J. Cook, asks to represent Talan, while fellow American Eric Sarin, Vik Sahay, works as her investigator. Kate hires English animal expert Dr. Gavin Flemyng, Simon Quarterman, with whom she had a romantic relationship five years earlier, to join the defense team. The defense begins to take shape as they interview Talan at the police station, but a struggle erupts, and Gavin is bitten by Talan while attempting to shield Kate.
The team travels to Talan’s remote house in the woods to interview his mother, Mrs. Gwynek, Camelia Maxim. She reveals she is originally from Romania and contends that Talan would have been too physically weak to commit the brutal murders because he suffers from a rare genetic condition passed down through the male line. She also claims the police are targeting Talan because the government wants to seize their land for use as a nuclear waste disposal site, a theory that places suspicion on authorities even as the case grows more volatile.
Gavin’s progress is complicated by personal tension—he flirts with Kate, triggering resentment from Eric—and he begins to feel increasingly ill after the encounter with Talan. The defense team starts to consider porphyria as a possible explanation for the strange affliction, and their hunch gains weight when Talan undergoes medical examinations in police custody. A stress test involving a strobe light triggers a violent reaction, and Talan exhibits a chilling, almost superhuman strength, slaughtering those in the room and escaping the building.
A citywide manhunt follows as Talan is tracked to an abandoned building. He is captured on camera transforming into a werewolf, then attacks an armed assault team, leaps from a height of eight stories, and evades capture. The pursuit intensifies until a second manhunt corners him, and he kills several police officers before being riddled with bullets and loaded into a police vehicle. Kate and Eric pursue the convoy, but the vehicle crashes, and Talan reappears, continuing his rampage.
Meanwhile, Gavin—now increasingly ill—investigates the Gwynek residence and discovers he shares the same affliction as Talan. He kills Mrs. Gwynek after realizing the family’s fate is tied to something worse, shaves off all his body hair, and gives in to his werewolf alter ego, howling at the Moon in his final form. In the ensuing chaos at the crash site, Talan kills Eric, and Gavin arrives to confront the other werewolf. The two engage in a brutal battle, ending when Gavin strangles Talan, seemingly killing him.
Kate finally confronts the transformed Gavin at gunpoint, but a sniper’s bullet—fired by Pistor from a police helicopter—strikes Kate in the gut. Gavin erupts in a fit of rage, hurling an assault-team member’s body into the helicopter, causing it to crash and killing Pistor. In the aftermath, news footage reveals that Kate survived, while Pistor’s involvement in a broader conspiracy to seize the Gwynek land is exposed. Talan’s body is never recovered, leaving him at large and continuing to be the source of terror, and Gavin’s true identity as a werewolf remains a carefully kept secret, with him stating that Talan is a werewolf.
