Ellen and Robert Bunting from London have fallen on hard times, finding themselves on the verge of bankruptcy. But one night, a mysterious stranger, who introduces himself as Mr. Sleuth, takes the lodge with them for a rent they so desperately need to survive. The Buntings ignore the lodger's mysterious experiments and late night walks, relaxing into their good fortune. However, at the same time Mr. Sleuth arrives, a serial killer, who calls himself "The Avenger," starts terrorizing the city of London, leaving behind several dead bodies of young blonde women.

Marie Lowndes Belloc (1868-1947) was a prolific English novelist, and sister of author Hilaire Belloc. Active from 1898 until her death, she had a literary reputation for combining exciting incidents with psychological interest. Lowndes Belloc produced mainly mysteries, well-plotted and on occasion based on real-life crime, though she herself resented being classed as a crime writer. Her best known work is The Lodger, a haunting mystery tale that revolves around the Jack the Ripper murders.