Captain slug, John Carradine, leads a small group of tourists aboard a fragile recreational boat. After engine trouble and a disturbing orange haze, nerves fray as Norman, Jack Davidson, grows increasingly abrasive, and the mood shifts from curiosity to unease. The night brings a collision with a hulking cargo ship that sideswipes their vessel, and a flare from the larger ship lights up a distant, rotting wreck resting on a reef—an eerie omen that dread has come ashore.
By morning, the Captain is missing and the boat is taking on water. The survivors evacuate in a lifeboat and head for a nearby island, hoping for safety. In daylight, the colossal wreck appears to have lay decomposing on the reef for decades, a forgotten relic of a world now stubbornly intruding on theirs. They press on exploring the island, stumbling upon a rundown hotel and a reclusive old man who seems to know more than he admits.
The old man insists there is no shipwreck on the island and appears alarmed by their tale. He recognizes the name they mention and goes down to the beach to investigate. Under the water, zombie-like men rise from the ship’s hull and begin marching toward the island, as if the ocean itself were clawing them back. As Dobbs, the boat's cook, gathers items to help prepare food, the zombies corner him in the shallows; he is dragged into danger and mangled after tumbling into a cluster of sea urchins. Rose, Brooke Adams, discovers his body while swimming, a grim clue amid the growing horror. Keith, Luke Halpin, finds a torn uniform bearing the insignia of the Nazi SS in his hand, a chilling link to the island’s buried past.
Inside the hotel, the host drops the larger truth: he was a Nazi commander in charge of the “Death Corps,” a band of zombies engineered to be super-soldiers who could thrive anywhere, with a specialized edge for aquatic operations. The creatures were meant to be a formidable weapon for the Nazis, but their control proved volatile and dangerous, even to their own troops. When Germany fell, he sank their ship and went into exile on the island. Now, with the ship’s return and the undead haunting the reef, the Commander himself fears what has been unleashed. He goes down to the beach to try to command the zombies, only to be overwhelmed by his own creation and drowned by the march of the living dead.
The survivors locate a boat the Commander had mentioned and attempt to steer it through the streams to open water, but they lose control and watch it drift away empty. Norman is drowned by a lurking zombie in a stream, while another closes in on Rose and she manages to kill it by ripping off its goggles. Chuck, Beverly, and Keith return to the hotel and barricade themselves inside the refrigerator unit, the cramped space sharpening fear into frayed tempers. The stress triggers a deadly fight: Chuck fires a flare gun and blinds Beverly, pushing the group toward desperate decisions. Keith and Rose escape to a furnace room, hiding behind metal grates while Beverly huddles in a closet. The zombies drown Chuck in a swimming pool outside, sealing their grim little fortress.
The next morning, Rose discovers Beverly dead, drowned in a fish tank, a haunting tableau of the island’s cruelty. Alone and desperate, Keith and Rose attempt an escape in a sightseeing rowboat with a glass bottom. The zombies attack; Keith manages to fend off one by tearing away its goggles, but a second zombie grabs him and drowns him as the dinghy breaches the reef and drifts free. Rose’s scream pierces the air as she steels herself against the horror she cannot outrun.
Two fishermen, Clarence Thomas, eventually pull Rose aboard their boat and carry her to safety. Back in the hospital, Rose lies in a bed and begins to write in a journal, only to reveal through her increasingly repetitive words that she has fallen into a state of madness, the island’s trauma echoing through her mind. The tale closes on a chilling note: the horrors of the Death Corps did not end with the ship’s sinking, but linger on, shaping what remains of the survivors’ lives—and what lies hidden beneath the quiet surface.
