Based on H.P. Lovecraft's novella of the same name, "Dagon" begins with Paul (Ezra Godden) foreshadowing what's to come when he dreams of a mermaid with sharp teeth. Shortly after, he wakes up on a boat that immediately wrecks. While he and his girlfriend try to find help, their friends left on the boat are attacked by a mysterious watery creature. It's not long before Paul's girlfriend disappears as well. Lost and without answers as to what to do next, Paul eventually winds up in a village full of half-fish, half-human creatures. It's here he learns the story of Dagon, a god-like being that initially helped the small town overcome their troubles. However, this creature has more sinister plans for the people in the village.