A group of scientists are working on a serum called Death One, which reanimates the dead. When Dr. Alan Holder (Robert Marius) and his assistant Norma experiment on a human corpse, the corpse becomes a zombie, prompting Dr. Holder to resign from the project. As he prepares to surrender the serum to waiting military officers, a small group of criminals ambush the center; all but one are killed, and the surviving criminal manages to abscond with Death One. During a chase, the container with the serum is shot out of his hand and breaks; as he tries to pick it back up, he accidentally touches the serum. He flees to the Sweet River Resort and settles in Room 4. General Morton (Mike Monty) promises Dr. Holder that he and his men will capture the criminal. By the time they catch up to him, however, he has already succumbed to the disease, but not before infecting a bellhop and killing a maid before finally cutting off his own hand in a failed attempt to stop the spread of the infection. General Morton orders the patrons and staff killed and buried in a mass grave, and condemns the resort; the criminal's remains are delivered to him and his right-hand men, Tracey (Bruno Mattei) and Cheney (Claudio Fragasso), and burned. As Dr. Holder and Norma fear, the ashes quickly infect the air, killing an entire flock of birds passing by.Meanwhile, a trio of GIs on vacation are on the lookout for some girls to make out with during their holiday; they find several on a nearby bus. Among the bus's passengers are Nancy (Ulli Reinthaler), Carol (Marina Loi), Lia (Deborah Bergamini), Suzanna (Mari Catotiengo), Jane, Jane's boyfriend Tom, and the bus driver, Joe. Not too far away, another passenger from the bus, Patricia (Beatrice Ring) and her boyfriend Glenn discover the dead birds and are promptly horrified as the birds reanimate and attack, with Glenn being pecked and clawed repeatedly. The birds then assault the bus while the GIs attempt to extricate everyone from it, but not before Lia gets bitten. Patricia and Glenn stop at a nearby garage but are forced to flee when a zombie wielding a machete attacks Patricia and the garage goes up in smoke. The GIs and the bus party make a stop at Sweet River Resort, with Bo (Massimo Vanni) and Carol going off to look for some help. When their car breaks down, Carol goes looking for some water but is attacked and mauled by the zombies. Bo tries and fails to save her and is forced to flee when more zombies emerge from the lake. He eventually joins up with Patricia and Glenn. On the way to Santa Monica Hospital, Glenn dies and reanimates as a zombie on the bridge. During the resulting confrontation with the living dead, Bo is killed, but Patricia escapes with her life. Meanwhile, Dr. Holder and his team start work on an antidote to counter the effects of Death One as General Morton's men start to eradicate the zombies.Back at the hotel, Jane and Tom go to the kitchen to look for some food but are ambushed and killed by a zombie head that had been resting in the freezer. Lia reanimates, kills and devours Susanna and almost kills Nancy before being thrown off the balcony and killed. Kenny (Deran Sarafian) and Roger (Ottaviano Dell'acqua) encounter Patricia as she arrives to try to break the news about Bo's demise, but the living dead start swarming the hotel. Kenny, Roger, Patricia, Nancy, and Joe kill as many zombies as they can before fleeing. After crossing the river, they are met by some of General Morton's men, who kill Joe. The other four escape as the final stage of General Morton's zombie eradication begins and Dr. Holder expresses his worries that the infection of the atmosphere may not be restricted to the island. Arriving at a nearby hospital, the four encounter a pregnant woman in labor. As Nancy helps deliver the newborn, Patricia engages in a final deathmatch against Glenn and beheads him, while Kenny and Roger have another run-in with General Morton's cleanup crew. Nancy is killed by the newborn, who turns out to be a zombie, and Kenny, Roger, and Patricia escape to find more zombies waiting for the kill. They make it to a helicopter, but only Kenny and Patricia are able to escape with their lives. Roger is attacked by the zombies while trying to join them and is subsequently killed by the cleanup crew. To Patricia's horror, the zombies have taken over; Blue Heart, the DJ who provided commentary for much of the film, even dedicates his next record to "all the undead around the world", having been infected himself. Upon hearing the broadcast, Kenny decides to return to the island, assuring Patricia that he intends to save what's left of humanity from the zombies.
Output: Question: What does Death One do?, Answer: Reanimates the dead