Julie Blair (Anne Kimball), a tourist visiting Mexico's Yucatan region, encounters deep-sea researcher Steve Dunning (Stuart Wade). They hear stories about people and animals that have disappeared from the area around the beach where they meet, but she doesn't believe the legend of a monster until she sees it herself. Then she must do her best to convince Steve and the authorities of what she saw. The creature turns out to be a mutation, probably spawned by recent atomic testing, and Steve must rescue her when she is caught by the monster as she searches for it.