A group of Viking women build a ship and set off across the sea to locate their missing menfolk, only to fall into the clutches of the barbarian Grimolts who hold their men captive and worship the sea serpent which overturned their ship.

Harold Gern, a shady businessman from New York, is spending a holiday in Puerto Rico with his attractive wife Evelyn. They are joined by Martin Joyce, Harold's lawyer, who has come to discuss the latest indictment. Harold invites him along on a boat trip during which all three try out some newly bought scuba diving equipment. When they resurface, they find out that the world has changed forever.

一个骗子决定撞死无能的船员，并将他们的死亡归咎于传说中的海洋生物，他不知道的是这个生物是真的，传说中的鬼海怪物真正现身了。