The Shadow over Innsmouth

"The Shadow over Innsmouth" is a horror novella by American author H. P. Lovecraft, written in November–December 1931. It forms part of the Cthulhu Mythos, using its motif of a malign undersea civilization, and references several shared elements of the Mythos, including place-names, mythical creatures, and invocations. The Shadow over Innsmouth is the only Lovecraft story that was published in book form during his lifetime.
The narrator is a student conducting an antiquarian tour of New England. He travels through the nearby decrepit seaport of Innsmouth which is suggested as a cheaper and potentially interesting next leg of his journey. There he interacts with strange people and observes disturbing events that ultimately lead to horrifying and personal revelations.