[1] In 1923,[2] an American named Delapore, the last descendant of the De la Poer family, moves to his ancestral estate of Exham Priory in England following the death of his only son during World War I.

This was stopped when Delapore's ancestor Walter killed his entire family in their sleep and left the country in order to end the horror, leaving the remaining human livestock and a surviving relative to be devoured by the rats inhabiting the city's cesspits.

Maddened by the revelations of his family's past, a hereditary cruelty, and his anger over his son's death, Delapore attacks Norrys in the dark of the cavernous city and begins eating him while rambling in a mixture of Middle English, Latin, and Irish, before devolving into a cacophony of animalistic grunts.

Long after writing "The Rats in the Walls", Lovecraft wrote that the story was "suggested by a very commonplace incident—the cracking of wall-paper late at night, and the chain of imaginings resulting from it.

Robert E. Howard, however, wrote a letter in 1930 to Weird Tales suggesting that the language choice reflected "Lluyd's theory as to the settling of Britain by the Celts"—a note that, passed on to Lovecraft, initiated their voluminous correspondence.

[12] In his essay, Lovecraft writes, "Later work of Mr. Cobb introduces an element of possible science, as in the tale of hereditary memory where a modern man with a negroid strain utters words in African jungle speech when run down by a train under visual and aural circumstances recalling the maiming of his black ancestor by a rhinoceros a century before."

Lady Margaret Trevor of Cornwall (mentioned in "Characters" above), the Elizabeth Bathory-like noblewoman who wed a scion of the De La Poer family in the fourteenth or fifteenth century, was apparently a direct ancestor of the narrator in another Lovecraft story, "Celephaïs".

(After the narrator of "Celephaïs" dies in the story, his dream-self lived on in the Dream-World, where he ruled a city and had the name Kuranes, and appears as a character in yet another Lovecraft work, "The Dream-Quest of Unknown Kadath", where it is confirmed that his ancestral home was on the coast of Cornwall.)

The story was rejected by Argosy All-Story Weekly before being accepted by Weird Tales; Lovecraft claimed that the former magazine found it "too horrible for the tender sensibilities of a delicately nurtured publick".

Equally important to the later development of the Cthulhu Mythos is that a reprint of this story in the June 1930 edition of Weird Tales inspired Robert E. Howard to write to the magazine praising the work.