A man fires a bullet into the head of a body wrapped in a sheet. He says to an off screen person, "The boat can leave now. Tell the crew."
Several days later, an apparently abandoned sailboat sails into New York harbor. Two officers of the harbor patrol board the boat to investigate and find the living quarters in squalor and disarray. They are suddenly attacked by a rotting, bloated zombie (Captain Haggerty
) which bursts from the hold, gorily killing one officer by biting his throat out, before being shot and propelled overboard by the second officer.
A local reporter named Peter West (Ian McCulloch
) is assigned by his hard-nosed editor (director Lucio Fulci
) to the case. That evening he meets up with Anne Bowles
) the daughter of the boat's missing owner. Anne has informed the police that she has not seen her father for the past three months since he traveled to the Antilles. Meanwhile at the morgue, the pathologist and his assistant are preparing to perform an autopsy on the dead police officer, when unknown to them, the dead body begins stirring...
The next morning, Peter and Anne fly to the Dominican Republic and meet an American tourist couple named Brian Hull (Al Cliver
) and Susan Barrett (Auretta Gay
) who are about to embark on a sailing tour of the Caribbean. Peter and Anne ask them to help them get to the island of Matul, where Anne's father was last heard from. Despite Brian's claim about warnings from the superstitious locals about Matul, the four of them agree to set off together for the island.
On Matul, tensions between Dr. David Menard
) and his contemptuous, highly strung-out wife Paola (Olga Karlatos
) are running high. She wants to leave island, terrified about reports of zombie attacks. He insists on staying to conduct research into the phenomenon, despite the fact that his medical mission is falling apart. Leaving her alone to drink her fears away at their isolated beach house, Menard drives in his jeep to his hospital, which is a ramshackle converted church buzzing with flies. Menard's superstitious Haitian assistant Lucas (Dakar
) insists that they leave, for all of the villagers of the nearby town are fleeing in fear of the rising of the dead. Menard scoffs at all this.
At sea, Susan goes on a scuba dive where she gets attacked, first by a shark, then by a strange aquatic zombie. Susan gets away, leaving the zombie to fight against the shark.
That evening, Paola Menard is alone in the house where she takes a shower to cool off in the hot and humid weather, when she hears a noise. Investigating, she is attacked by a marauding cadaver (unseen except for a rotting, outstretched hand). As she struggles to barricade herself into her bedroom, the zombie smashes its arm through the door and grabs her by her hair. Her head is slowly pulled onto the shattered doorframe, and she dies a horrible death as her right eye is impaled on a spike of slatted wood as she's pulled out the door.
The next morning, Anne, Peter, Brian, and Susan arrive off the coast of Matul where they find out that their boat has been damaged by the shark attack. They anchor in a bay off the island and send up distress flares. Menard answers their distress call as Luca and Menard's personal nurse (Stefania D'Amario
) bury more dead bodies, victims of a mysterious virus that's killing the islands residents and resurrecting them as zombies. The survivors are forced to shoot each corpse in the head to prevent them from reviving before burying them. On the drive back to the hospital, Menard tells his four visitors that Anne's father (Ugo Bologna
) died three months earlier from the strange disease plaguing the island. Menard also tells the disbelieving visitors that the zombie epidemic, so far on the other side of the island, is blamed by the locals on the voodoo curses of a evil witch doctor. When they arrive at the hospital, Menard's nurse informs him that a friend has been taken ill. Menard then asks Peter, Anne, Brian, and Susan to drive over his house and check on the safety of his wife. Menard looks at his friend, Fritz, who claims he was bitten by a zombie in the village. Menard orders Lucas to lock all the doors and windows, now aware that the zombies are approaching this end of the island.
Meanwhile, Peter, Anne, Brian, and Susan arrive without incident at the Menard cottage and upon entering they make a horrific discovery. The dead body of Mrs. Menard is sprawled out outside the bedroom door, half-eaten, surrounded by a small group of zombies who are gorging on her remains. Revolted, they fight their way past a group of slow-moving, staggering zombies and drive back to the hospital. But on the road, a zombie wonders into their path, and the jeep is damaged as they swerve into the dense tropical undergrowth. Peter's left ankle is broken upon the impact, but the group decide they must make it back to the hospital.
A little later, the group stops for a rest in a small jungle clearing which they see is an old cemetery for the Spanish Conquistadors. As Peter and Anne lie down on the ground for a rest, the buried Conquistadors emerge from the soil. One of them grabs Anne by her hair while another grabs Peter by his broken ankle. The two of them break free, but Susan is not so lucky. Frozen in terror by the sight of a large, worm-faced cadaver (Ottaviano Dell'Acqua
), she dies as it bites her throat out before it's dispatched by Peter and Brian, who bash the creature's head in. The three survivors are now obliged to make the journey back to the hospital as the living dead erupt from their tombs all over the island, as well as stalk the deserted shanty village nearby.
At nightfall, Anne, Peter, and Brian finally arrive back at the hospital. Dr. Menard tends to Peter's broken ankle, while Brian helps Lucas and the nurse barricade the doors and windows. Menard is informed to his wife's fate, but does not comment on it. Instead, he raves about his failed efforts to find a scientific explanation for the walking dead and their instinct to feed on human flesh. Suddenly, a large group of the tottering, implacable creatures try to batter down the boarded up front door. Menard and the group begin to construct barricades as well as make Molotov cocktails from the kerosene tanks. However, the hospital's sick patients are dying and coming back as zombies, making the hospital under attack from inside and out. Menard is the first to go when he gets his face ripped off by the zombie Fritz, before it's killed by Brian with a gunshot to the head, the only way of killing the reanimated zombies. Lucas is next when he gets part of his arm bitten off by another zombie. The nurse is then killed by the zombie Lucas, who then attacks Anne but gets shot dead by Peter. The mob of zombies finally breaks down the front door, and a climactic battle between the three survivors and the foul creatures begins, with fire apparently the only effective weapon against the slow moving, walking stiffs. With the hospital now on fire from the exploding Molotov cocktails, Anne, Peter, and Brian are forced to flee from the burning building out the back door. But outside, Brian comes face to face with the walking corpse of the resurrected Susan. He succumbs to emotion and gets badly bitten on his arm as a result. The zombie Susan is immediately shot and killed by Peter, and the trio run for the beach with some zombies not far behind.
As dawn breaks, the gerry-rigged boat limps back out to sea. Brian sinks into unconsciousness, terminally sick from the zombie bite, and soon dies. Peter and Anne lock the dead Brian up in the boat's cabin, for Peter wants the dead Brian as proof to the authorities that the whole experience happened. Turning on the radio, Peter and Anne listen in disbelief as a radio announcer explains about a zombie epidemic gripping New York City apparently brought on the by zombie from the opening scene. Down in the cabin, Brian's re-animated corpse frantically tries to get out of the hold it is locked up in.
In New York City, a long line of freshly dead zombies are seen, slowly marching across the Brooklyn Bridge into Manhattan.