1897 – A cargo ship is heading from Romania to England. When it is found on the shores, it is derelict with no survivors onboard. A lighthouse crew finds the wreckage, and they recover a captain’s log, detailing an account of what led to the crew’s demise.
Four days earlier, Captain Elliot (Liam Cunningham) and his first mate Wojchek (David Dastmalchian) are looking for crew members to board the Demeter to sail to England. They are approached by a doctor named Clemens (Corey Hawkins), who previously studied at Cambridge. However, Wojchek turns him down in favor of three other men. Clemens follows anyway.
As the men are gathering their cargo onto the ship, one of the men gets spooked when he sees a crate that has the symbol of a dragon on it, causing him to lose his grip on it. The crate slips and nearly crushes Elliot’s grandson Toby (Woody Norman), but Clemens pulls him out of the way in time. The man leaves, fearing that the dragon symbol is a bad omen. Elliot is thankful to Clemens, and he boards the ship, along with crew mates Abrams (Chris Walley), Olgaren (Stefan Kapicic), Petrofsky (Nikolai Nikolaeff), Larsen (Martin Furulund), and Joseph (Jon Jon Briones).
Toby gives Clemens a tour of the boat, showing him the livestock and his dog Huckleberry. Clemens later dines with the crew, saying that his desire is to understand the way the world works. Meanwhile, the crate with the dragon symbol begins to move and falls over, and something appears to emerge from it.
The crew makes their way to England, but they later discover that something violently killed Huckleberry and the livestock. Toby is devastated for Huck’s loss and because he was entrusted by Elliot to look after the animals, but Clemens comforts him. After the men toss the animals overboard, they investigate the cargo and find a woman (Aisling Franciosi) just barely alive having been stowed away in one of the crates. Clemens administers blood transfusions to keep her stable. Petrofsky makes derogatory comments regarding Clemens and the woman, and when Clemens attempts to retaliate, Larsen holds a knife at him. Toby later tells Clemens that the woman has been speaking slightly and that her name is Anna.
At night, Petrofsky is keeping watch on deck while the rest of the crew sleeps. He hears a knocking sound and goes to investigate. Petrofsky then sees a sickly-looking creature (Javier Botet) crawling on deck. Before he can do anything else, the creature lunges at Petrofsky and slashes his throat with its claws before proceeding to suck his blood out.
The crew becomes weary when they find Petrofsky’s blood smeared across the deck. Wojchek initially accuses Clemens, even though he was the one who reported Petrofsky’s demise. Later at night, Olgaren and Larsen are keeping watch on deck, when the same creature attacks Larsen and drags his face across the deck before devouring him. Olgaren climbs high up to escape the creature, only for it to follow and bite into Olgaren’s head, leaving him alive but gravely wounded.
Olgaren is strapped to a bed to be tended to, but as night falls, he becomes free from his bindings and goes after Toby, as he has now become a bloodthirsty drone. Toby hides in the captain’s quarters and locks himself in there. The rest of the crew realizes something is wrong and heads below deck. They subdue Olgaren and try to break through the door, but Toby is being stalked by the creature. Anna comes by and grabs a rifle to blow the lock off the door, but by then, Toby has already been attacked by the creature, who has taken most of his blood.
Abrams is left to keep watch on the deck at night. Joseph knocks him out and tries to take a lifeboat to get off the ship and away from the creature. Unfortunately, it can fly and manages to find Joseph and kill him, letting the boat come back to the Demeter empty but bloodied.
While Toby is placed in care, Olgaren is strapped to the mast of the ship. He claims he can hear every sound of the wind, ocean, and the blood pumping in everyone’s veins. The sun begins to rise, and Olgaren complains that he feels a burning sensation. The sunlight touches his skin, causing him to violently combust in agony before Wojchek shoots him in the head. Anna talks to Clemens and explains that she knows what is the cause of all this. In her village, she lived near a castle where the creature dwelled. He is none other than Dracula. He has bitten Anna and was planning to use her as blood rations, but the transfusions that Clemens gave her prevented her from turning like Olgaren did. Elliot wants to stop at the next port for the crew’s safety, but they protest because it would mean they would not get a bonus payment as was promised.
Fearing Toby will suffer the same fate, the crew wraps him in a sheet and prepares to throw his body into the ocean. After Anna says a prayer for him, Elliot becomes delusional in his grief and thinks Toby is moving. He opens the sheet, and Toby becomes vampiric. The sunlight burns him too, and Elliot suffers burns on his skin from touching the boy. They throw him into the ocean where he ultimately dies, and Elliot is left in despair.
As the Demeter gets closer to England, the crew fears of what may happen if they bring Dracula with them. Elliot becomes more delusional, believing that they can use Dracula to revive Toby, but Anna talks him down from it. The crew resolves to make their final stand with Dracula by bringing him down with the ship, even though Wojchek doesn’t want to because he claims the ship is his home.
Night falls, and the crew gets ready for Dracula’s appearance. The vampire beast swoops by and kills Abrams first while Elliot plans to go down with the ship. Wojchek falls through the deck and breaks his leg, and Dracula kills him before going after Elliot. Clemens attempts to fight Dracula, but the villain grabs Clemens by the throat. He says he does not fear him, and the vampire speaks for the first time, saying “You will.” Anna grabs a rifle and fires at Dracula, then cuts the mast down so it can pin him down. She and Clemens make it off the Demeter as it crashes against the shores in England where the lighthouse crew finds it, and Dracula flees.
The morning comes, and Clemens sees that Anna is slowly reverting to her vampirism. While he suggests making another transfusion, she says it will only prolong the inevitable. She bids him farewell and separates from him as the sun begins to rise, and she burns to death.
Clemens arrives in London, while the entire crew of the Demeter is reported dead. Clemens goes to a nearby pub to seek out the abbey where Dracula once lived, and then hears the same knocking sound from the ship. The evil vampire is there in London disguised as a man, carrying the same wolf cane he came onboard with. Clemens follows Dracula outside and vows to not rest until he sends the creature back to Hell once and for all.