"The Thing on the Doorstep" is a horror short story by American writer H. P. Lovecraft, part of the Cthulhu Mythos universe.

A few months later, Derby shows up at Upton's door and says he has found a way to keep Asenath away and to stop her from using his body, implying some sort of spell or ritual.

Upton receives another visit from Derby, who begins raving about his wife and father-in-law and how he can still feel her, him, it, clawing at his mind while he sleeps, trying to get hold of him.

The note implores Upton to go to the sanitarium to kill Derby, who has now been permanently possessed by Ephraim's soul the way he imagines the original Asenath once was.

Lovecraft's depiction of Derby's childhood is considered to be in large part autobiographical:[3] Perhaps his private education and coddled seclusion had something to do with his premature flowering.

His health had improved, but his habits of childish dependence were fostered by over-careful parents, so that he never travelled alone, made independent decisions, or assumed responsibilities.It is considered unlikely, however, that the typically self-deprecating Lovecraft was thinking of himself when he described Derby as a child prodigy and young literary sensation: He was the most phenomenal child scholar I have ever known, and at seven was writing verse of a sombre, fantastic, almost morbid cast which astonished the tutors surrounding him... Young Derby's odd genius developed remarkably, and in his eighteenth year his collected nightmare-lyrics made a real sensation when issued under the title Azathoth and Other Horrors.The title of Derby's book suggests that Lovecraft had Clark Ashton Smith in mind, who won acclaim at the age of nineteen when he published a book of poetry called The Star-Treader and Other Poems (1912).

Another possible model is Alfred Galpin, a friend of Lovecraft's who was eleven years his junior, whom he described as being "immensely my superior" in intellect.

[4] In writing that Derby's "attempts to grow a moustache were discernible only with difficulty", Lovecraft evoked his protégé Frank Belknap Long, whom he frequently teased for the same reason.

[4] Derby's correspondence with "the notorious Baudelairean poet Justin Geoffrey" is an homage to the Robert E. Howard Cthulhu Mythos story "The Black Stone" (1931).

"Where cosmic forces usually overtake the typical Lovecraft hero such as Peaslee by chance, here Derby has only his own weak personality to blame for his falling victim to his wife's nefarious designs.

[7] In Fritz Leiber's story "To Arkham and the Stars" (1966), Upton is credited with designing Miskatonic University's new Administration Building and the Pickman Nuclear Lab, described as "magnificent structures wholly compatible with the old quadrangle."

Albert Wilmarth remarks in the story that Upton "has had a distinguished career ever since he was given a clean bill of mental health and discharged with a verdict of 'justified homicide'".

Combined with the fact that her mother was Ephraim's "unknown wife who always went veiled", there is a strong suggestion that Asenath is a Deep One hybrid of the sort described in Lovecraft's The Shadow over Innsmouth.

"[9] Peter Cannon writes that Asenath Derby makes "The Thing on the Doorstep", "the only Lovecraft story with a strong or important female character"—although the question is complicated by the tale's "gender-swapping situation".

Lin Carter likewise dismisses the tale as "curiously minor and somehow unsatisfying...a sordid little domestic tragedy...wholly lacking in the sort of cosmic vision that makes Lovecraft's best stories so memorable".

[14] This is the only work of Lovecraft's included in the Library of America's 2009 anthology American Fantastic Tales: Terror and the Uncanny from Poe to the Pulps.

In July 2022 it was announced that Joe Lynch would be directing an adaptation of the story, titled Suitable Flesh, starring Heather Graham, Bruce Davison, Johnathon Schaech and Barbara Crampton.