The narrator is a student on an antiquarian tour of New England. He sees a piece of exotic jewelry in a museum, and learns that its source is the nearby decrepit seaport of Innsmouth. He travels to Innsmouth and observes disturbing events and people. A local resident tells him a horrifying story of aquatic monsters who can interbreed with humans to produce amphibian hybrids. The student is then tricked into staying overnight in the town.