When Sean Branch sails toward the Bahamas, he thinks it is to enjoy a week of diving with his wife and friends. He soon realizes that Robert, their hired Captain, is not very accommodating. He is secretive about his past and his reasons for leading them to a cluster of uncharted islands. On the morning of the second day, Robert confesses his secrets after he kills a young temptress. He has hunted the animals for years and he uses his customers to fund his search. Sean confronts him, and begins to understand why the creatures are a myth. They want their seclusion, and to guarantee it, they may not allow him to leave the bay alive.