Paul Marsh dreams of encountering a mermaid with razor-sharp teeth while exploring an underwater cave.

He awakens on a boat off the shores of Spain, where he is vacationing with his girlfriend Barbara and their friends Vicki and Howard.

While Howard stays with her, Paul and Barbara take the lifeboat to the nearby fishing town of Imboca.

After failing to find either Howard or Vicki, Paul goes to the hotel where Barbara supposedly stays, but she isn't there.

Awakened by a large gathering of strange, fish-like people approaching the hotel, he is forced to flee.

He escapes the tannery by starting a fire and finds momentary safety with an old drunkard named Ezequiel, the last full-blooded human in Imboca.

Orpheus's first offerings to Dagon brought Imboca enormous wealth in the form of fish and gold.

However, Dagon soon demanded blood sacrifices and human women to breed with, which the villagers and Cambarro blindly complied.

Ezequiel takes Paul to the Mayor's manor, so he can steal the town's only car belonging to Xavier Cambarro, Orpheus's grandson.

Cornered, he flees into the manor and finds a beautiful woman named Uxia, the mermaid from his dreams.

When Paul reaches the church, he discovers a hidden passage leading to an underground ritual chamber.

As a congregation of Imbocans watches, Uxia offers a naked Barbara handcuffed to a trapeze to Dagon, lowering her into a deep pit leading to the sea.

[5] On April 8, 2018, it was announced that the film would be released for the first time on Blu-ray, as a part of a collector's series by Vestron Video.

[7] Marjorie Baumgarten from Austin Chronicle gave the film 3 out of 5 stars, calling it "horror so extreme that it borders on camp", further stating that it was "hampered by some clunky scripting [...] and middling performances.

"[13] Nick Hartel from DVD Talk praised the film, calling it director Gordon's all-time best work, and the best Lovecraft adaptation.