Set in a foggy, atmospheric London, the plot revolves around a series of gruesome murders terrorizing the city. Jack the Ripper appears to be on the loose, sending waves of fear through the community. Among the worried citizens are Ellen and Robert Bonting, who are struggling financially and decide to take in a lodger named Mr. Slade. Slade is a mysterious and strangely aloof man who rents their attic room. Ellen, curious and suspicious, soon begins to notice odd behaviors and finds herself questioning Slade’s true intentions. Meanwhile, Inspector John Warwick is relentlessly on the hunt for the killer, weaving through the dark and narrow streets of London in search of clues.

As the story unfolds, the tension within the Bonting household grows thicker. Mrs. Bonting becomes more and more wary of Slade, especially as he exhibits peculiar habits and increasingly erratic behavior. Slade's late-night excursions only escalate her suspicions. While the city remains haunted by each new killing, Ellen's anxieties align with her husband's initial skepticism turning into fear. Warwick, driven by a mix of professional duty and personal vendetta, closes in on potential suspects, leading to climactic encounters and revelations. The eerie atmosphere and psychological tension build until it peaks midway through the narrative.