Gilman begins experiencing bizarre dreams in which he seems to float without physical form through an otherworldly space of unearthly geometry and indescribable colors and sounds.

Several times, his dreaming self encounters bizarre clusters of "iridescent, prolately spheroidal bubbles", as well as a rapidly changing polyhedral figure, both of which appear sapient.

Gilman's odd experiences seem to escalate as he dreams that he signs the "Book of Azathoth" under the commands of Keziah, Brown Jenkin, and the infamous "Black Man."

He thwarts Keziah by strangling her with the chain of a crucifix, but Brown Jenkin bites through the child's wrist to complete the ritual and escapes into a triangular abyss.

The skeleton of an enormous deformed rat with hints of human or primate anatomy is soon discovered within the attic's flooring; this baffles academia and disturbs the demolition workers so greatly that they light thanksgiving candles within a nearby church in celebration of the creature's demise.

Formerly of Haverhill, Massachusetts, Walter Gilman came to Miskatonic to study "non-Euclidean calculus and quantum physics", which he linked to the "fantastic legends of elder magic".

She later disappeared mysteriously from Salem Gaol, leaving behind "curves and angles smeared on the grey stone walls with some red, sticky fluid" that were inexplicable even to Cotton Mather.

Gilman comes to suspect that Mason—"a mediocre old woman of the Seventeenth Century"—had developed "an insight into mathematical depths perhaps beyond the utmost modern delvings of Planck, Heisenberg, Einstein, and De Sitter."

Mason's familiar, "a small white-fanged furry thing", "no larger than a good-sized rat", which for years haunts the Witch House and Arkham in general, "nuzzl[ing] people curiously in the black hours before dawn".

He merely pointed to a book of prodigious size which lay open on the table....This character is later identified as "the immemorial figure of the deputy or messenger of hidden and terrible powers—the 'Black Man' of the witch-cult, and the Nyarlathotep of the Necronomicon."

A later reference to markings on the floor Gilman finds among his own footprints suggest the Black Man has cloven hooves instead of feet, a common feature of the Devil in folklore.

[3]: 128 "The Dreams in the Witch House" was likely inspired by Willem de Sitter's[4] lecture The Size of the Universe, which Lovecraft attended three months prior to writing the story.

Several prominent motifs—including the geometry and curvature of space and using pure mathematics to gain a deeper understanding of the nature of the universe—are covered in both Lovecraft's story and de Sitter's lecture.

[citation needed] An H. P. Lovecraft Encyclopedia says that "The Dreams in the Witch House" was "heavily influenced by Nathaniel Hawthorne's unfinished novel Septimius Felton".

"[6] Steven J. Mariconda called the story "Lovecraft's Magnificent Failure... its uneven execution is not equal to its breathtaking conceptions, which are some of the most original in imaginative literature".

[7] Peter Cannon claims that "most critics agree" that "The Dreams in the Witch House" ranks with "The Thing on the Doorstep" as "the poorest of Lovecraft's later tales.

"[9] An H. P. Lovecraft Encyclopedia complains that "[w]hile the tale contains vividly cosmic vistas of hyperspace, HPL does not appear to have thought out the details of the plot satisfactorily...