A woman running naked through the jungle on Blood Island is killed by a green-skinned beast that resembles a man. At the same time, a ship arrives at the island carrying American pathologist Bill Foster, who is investigating a strange chlorophyll disease among the islanders; Sheila Willard, who has come...
A woman running naked through the jungle on Blood Island is killed by a green-skinned beast that resembles a man. At the same time, a ship arrives at the island carrying American pathologist Bill Foster, who is investigating a strange chlorophyll disease among the islanders; Sheila Willard, who has come to Blood Island seeking to reunite with her father; and Carlos Lopez (Ronaldo Valdez), who wants to get his mother, Mrs. Lopez, to move off the island. The captain of the ship claims that the island is cursed and tells a story of a man they picked up on a raft who bled green blood before he escaped into the sea.
Sheila discovers that her father is a hopeless alcoholic. Mrs. Lopez does not want to leave the island, even though her husband, Don Ramon Lopez, died there recently under mysterious circumstances. The suspicious Dr. Lorca will not reveal any details about Don Ramon's death to anyone. When Foster and Lopez exhume the grave of Don Ramon, it is empty.
Rumors abound about a green-skinned monster with chlorophyll blood that has been killing the local natives. One night, a native with green sores on his body tries to break into the government house, but runs off into the jungle when he is confronted. Sheila is attacked in the jungle by the chlorophyll monster, but manages to escape when an unfortunate native who comes to her rescue is gruesomely mutilated by the creature. Sheila and Dr. Foster fall in love during their stay on the island.
It is revealed that Dr. Lorca has been experimenting on the natives, including the unfortunate Don Ramon, who had sought Dr. Lorca's serum as a treatment for his cancer, but was turned into a monster instead. They learn that Don Ramon is actually the green-blooded beast that has been killing people on the island. Don Ramon kills his wife, and almost kills his son Carlos, but at the last moment a glimmer of humanity returns to the creature and realizing what a monster he has become, he attacks Dr. Lorca in his hidden lab instead. A fire breaks out in Lorca's lab, resulting in a huge explosion, killing Dr. Lorca, his assistant and the monster.
Sheila, her father, Dr. Foster and Carlos all return to the ship, glad to finally leave Blood Island. But as the ship leaves port, a grisly hand appears from underneath a boat tarp, dripping green blood.
