The story begins on a stormy night with Emmett Glanton driving his Model T when he is suddenly forced to halt by Joshua, a mentally unstable worker, exhibiting unusual and threatening behavior. Joshua warns Glanton not to proceed to their neighbor, John Bruckman's house, despite having been called over urgently. Ignoring the warning, Glanton heads to Bruckman's house, where he finds himself part of an impromptu and suspicious marriage arranged by Bruckman between him and his niece, Joan Zukor, seemingly to protect himself from an ominous pact he had with a cult known as the Black Brothers of Ahriman.

The narrative quickly escalates as Joshua's violent tendencies are revealed, and he confesses to murdering his own brother. Glanton, now married, leaves Bruckman's house but soon learns that Bruckman has been gruesomely tortured and killed by the cult for betraying their secrets. The cult's plan to sacrifice Joan as part of their dark rituals unfolds, forcing Glanton into a desperate rescue.

Glanton returns to his ranch to find his worker, Sanchez, murdered and his new wife, Joan, kidnapped. Following clues, he confronts the cult members in a climactic showdown, where Joshua, despite being fatally wounded, aids Glanton unintentionally by attacking the cultists, resulting in their deaths from an electrified ritual site.

The story ends with the dawn breaking, symbolizing a new beginning for Glanton and Joan, who have survived the horrors of the night and are now bonded by their shared ordeal.