The story begins with the narrator, Steve, recounting an unsettling experience he shared with his friend John Harker in San Antonio. One late night, as they walked past a rambling, two-story boarding house, Harker suddenly became terrified, claiming to have seen a shocking murder through an upstairs window. He described a headless, bloody man crumpled on a bed.

Despite their immediate efforts to investigate with the help of a policeman, they found the room empty and undisturbed. The landlady and the policeman dismissed Harker's vision as a hallucination, possibly induced by alcohol or fatigue. Harker himself, though deeply shaken, began to doubt his own sanity.

Some months later, Steve and Harker met again, and Harker revealed that he had moved into the very boarding house where he had seen the supposed murder. Steve felt an uneasy thrill but said nothing.

A year later, on the exact anniversary of the incident, Steve walked past the same house at the same time of night. He glanced up at the window and saw a flash of red, a figure huddled on the bed. Gripped by fear but driven by curiosity, he knocked on the door and asked the landlady to take him to Harker’s room.

When they entered the room, they found Harker’s decapitated body exactly as he had described seeing it a year earlier. The scene was horrifyingly real, with blood everywhere and Harker’s severed head on the floor. The landlady fainted at the sight, and Steve was overcome with shock.

The murderer, a maniac who had escaped from a nearby asylum, was soon captured. In his ravings, he described how he had entered through the window and decapitated Harker with a meat cleaver, exactly as Harker had envisioned. The maniac’s confession confirmed that Harker had witnessed a premonition of his own death a year in advance.

The story concludes with Steve reflecting on the ghastly experience, expressing his ongoing fear of looking into lighted windows at night, fearing what visions they might reveal.