The story of The Singing Detective unfolds in three time periods: a 1980's hospital ward; The Forest of Dean (and later London) in the 1930's; and a film-noir fantasy London of the 1940's. The link between these 'worlds' and the protagonist of the story is Philip Marlow, the writer recovering from psoriasis in the hospital. The story follows his recovery from his skin condition and parallel assimilation of a childhood trauma he suffered in the 1930's. The Forest of Dean parts of the story are Marlow's childhood memories. The young Philip, it is revealed, witnessed his mother's adultery with Raymond Binney and took revenge upon his backward son Mark by implicating him for a schoolroom crime he committed. The film-noir fantasy is from a novel he wrote entitled 'The Singing Detective' in which the character, Mark Binney, hires the help of the detective, Philip Marlow, to help him escape being framed for a murder.

The story is structured as a detective story on many levels. First we have the 'fictional' detective uncovering the murderer of the body in the river, secondly there is the psychiatrist, Dr. Gibbon's, detective work of uncovering Marlow's childhood trauma. Parallel to this is Marlow's own voyage of discovery into his past. On other levels there is the search for who defecated on the teacher's desk, the crime for which Mark Binney is punished, and Reg, a patient on the ward, who is reading Marlow's book in pursuit of 'whodunit'. In all cases it is Mark Binney who appears to be the most likely suspect but Marlow who transpires to be the true culprit.