John and Kathleen Strauss are a couple attempting to uncover the secret to John's rare blood disease. They encounter Dr. Marlowe, who is intrigued by the case. They are unaware that the island which they are about to set foot upon is home to the Van Dam family, mutant-like creatures who have become deformed and bloodthirsty from centuries of inbreeding. Their mutation began with their relative Eva Van Dam, who had a Incest between twins relationship with her twin brother. Also, they are fully functioning hermaphrodites, capable of reproducing with themselves. They need to survive on (dead or alive) human flesh.