The investigators receive a letter from the country’s greatest occult scholar, Étienne-Laurent de Marigny. It mentions the unsolved murder of a reporter, a possible conspiracy, and a peculiar drawing found clutched in the dead man’s hand. Being occult in nature, but unable to devote the time and effort needed to identify it, he requests their consultation.

A warehouse full of dynamite and the dead. A weapon that throws lightning. A dog that barks at a professor. And in a roofless shack in the woods, the order for what is coming tomorrow night.

The investigators receive a letter from the country’s greatest occult scholar, Étienne-Laurent de Marigny. It mentions the unsolved murder of a reporter, a possible conspiracy, and a peculiar drawing found clutched in the dead man’s hand. Being occult in nature, but unable to devote the time and effort needed to identify it, he requests their consultation.

The fall term opens, and the university turns a cold shoulder to the survivors of Cobb's Corners. A dean lays down the law; a president bars his doors. In the margins of three old books, a dead man's handwriting spells out what he knew, and how late he learned it. A girl buys a dog because the books say the things are afraid of them. A gangster in a penthouse restaurant explains, over lobster and champagne, exactly how badly he needs his cousin back. And on a circled street name in a missing detective's notepad, the trail leads to a warehouse where a key fits a lock it was never meant to fit.

The expedition returns to Arkham to find the students who came back from Cobb's Corners are not themselves. A professor locks his office door and names the thing that wears human faces. A woman in New York lays out ten cards and reads the shape of a dark star. And in an attic on West Pickman Street, the man who led them into the hills is found with a bullet in his skull and the window open behind him.

Disgraced and disbelieved, the survivors are shipped home to Miskatonic — where their friends walk the same halls in the same faces, eating the same food with the wrong hands. A girlfriend comes looking for the boy she loved and finds a stranger who speaks in someone else's voice. A professor who was meant to be on the expedition meets the priest who went in her place and does not recognise him at all. And in a locked office on the second floor of the English department, a man who has seen these things before tells a Swiss mountaineer that they are not safe. None of them are safe.

The fog closes over Broken Hill, and the ground beneath the camp begins to hum. By midnight, something has come down out of the dark that is not a falling star — and it has come for its own. By dawn, the friends who were taken have walked back into the sheriff's office alive, and wrong.

The flood recedes and the flower bed gives up its dead. On a hill where no bird sings, the survey team uncovers a whole people buried in a single grief-stricken pit, and a schoolteacher shows a priest what the town's children have been drawing. By nightfall the fog is rising on Broken Hill.