A spectral entity known as the October Man begins to stalk the streets of London, leaving a trail of fear and death. Peter Grant, a probationary constable in the Metropolitan Police, finds himself drawn into the supernatural underbelly of the city when he encounters a ghost. This ghost, the October Man, is a malevolent force tied to the city's history and its darker aspects. Peter must learn to navigate the world of magic and spirits, guided by the enigmatic wizard Nightingale, to understand and ultimately stop the October Man before he claims more victims.

The Rivers of London series is generally well-received for its unique blend of urban fantasy, police procedural, and British humor. Readers often praise Ben Aaronovitch's witty prose, intricate world-building, and the compelling character of Peter Grant. The series is noted for its clever integration of London's history and mythology into its supernatural elements. This particular installment, 'The October Man,' is often highlighted as a strong entry that deepens the mythology and Peter's role within it.