In late 1945, as World War II draws to a close, a life raft drifts across the cold North Atlantic, carrying the survivors of a hospital ship that was torpedoed and sunk by a German submarine. On board are the American cook Bigelow, the American mechanic Jackson, the British nurse Jane Prescott, the British codebreaker Gerard Faraday, the Australian soldier Sinclair, the Russian sniper Alexander Teplov, and Malone, the American captain of the hospital ship, all adrift after days without food. A Nazi minesweeper drifts by, and the group boards the vessel, hoping for rescue, only to witness tragedy as Malone falls while climbing aboard and is killed by the ship’s propellers. The survivors push forward, scouring the seemingly-abandoned hull for signs of life or salvation.
Sinclair, Teplov, and Bigelow make their way to the bridge and discover the steering wheel chained in place, with the mutilated body of a German crew member nearby. Down below, Jackson checks the engine and uncovers a grim scene: corpses burned in the furnace-stoked spaces and a boiler that has failed, threatening an imminent explosion if the engine remains running. He quickly shuts it off, leaving the ship dead in the water, a precarious floating time bomb in the vast ocean.
A frightened young girl emerges from the galley, speaking Romanian and introducing herself as Mya. She leads the survivors to a heavy locked door further below deck. When they pry it open, they find a surviving German crew member who becomes terrified at the sight of Mya and attempts to kill her with his Luger, accidentally killing Jackson instead. Teplov steps in and ends the German’s life, while Bigelow and Sinclair inspect the room where the German had holed up. They uncover several large wooden boxes, a box of gold, and a mysterious container filled with crucifixes and glass-like grenades filled with water. The group then explores the captain’s quarters and finds photographs and documents showing Nazi soldiers unearthing ancient artifacts, including sarcophagi and a thick tome depicting monstrous creatures.
Driven by greed, Bigelow returns to the storage area and pries open one sarcophagus, only to disturb a slumbering, bat-faced creature that awakens and kills him. Sinclair, realizing the danger, battles to keep the creature sealed within the storage room, slamming the door to trap it inside. The creature’s awakening triggers a chilling transformation in Mya, revealing that she is of the same otherworldly species; she lunges at Jane, but Teplov intervenes and shoots her, driving her back.
Faraday slips away to the radio and contacts a German force, offering British information in exchange for rescue, but Mya attacks him before any deal can be made. Sinclair, Teplov, and Jane study the documents and the film in the captain’s cabin; Teplov recognizes the depicted monsters as Strigoi—legendary beings said to feed on blood, capable of shapeshifting and bending minds. In the storage room, the male Strigoi awakens the female, and the German survivor’s bite on Faraday allows the Patriarch to psychically control him. The survivors manage to kill the possessed Faraday and then lure Mya into a trap in a gasoline-filled room, where she is burned to death. As she burns, the Patriarch forms a psychic link with Jane through the bite she received earlier and compels her to help free him and the Matriarch from their confinement, ultimately biting Jane’s neck in the process.
Teplov returns to the storage area to arm himself with the holy weapons kept there, but is ambushed by the Patriarch and bitten in the neck. He manages to escape and teams up with Sinclair to confront the threats, and together they kill the Matriarch by decapitation with an axe after a tense firefight. With a distant ship approaching, they resolve to destroy the Nazi threat by detonating a warhead in the munitions storage, sacrificing themselves to end the menace. Teplov stays behind to detonate the warhead, using a crucifix for protection, while Sinclair and Jane escape in a frantic dash toward safety.
As the explosion rips through the vessel, the approaching British ship finally nears. Sinclair plunges back into the water to rescue Jane, who seems momentarily lucid, but upon regaining consciousness she reveals she has been infected by the Patriarch. She bites Sinclair’s neck, killing him and letting the infection spread, and then she hides her own infection to be rescued by the unsuspecting British sailors. The North Atlantic night closes in around the wreckage as the survivors’ fates hang in the balance, testing the boundaries between courage, humanity, and the creeping horror that stalks the end of war.
