Detective Inspector Slack is an acquaintance of Miss Marple.
In The Murder at the Vicarage, Inspector Slack arrives in St. Mary Mead to investigate the murder of Colonel Protheroe. He comes by car from Much Benham, which is two miles away. He is described as "a dark man, restless and energetic in manner, with black eyes that snapped ceaselessly". Reverend Clement feels that Slack's manner is rude and overbearing.
- The Murder at the Vicarage (1930)
- The Body in the Library (1942)
- The Case of the Perfect Maid (short story) (1942)
- Tape-Measure Murder (short story) (1950)
- 4.50 from Paddington (1957)
- In They do it with Mirrors (1991), Slack is a Chief Inspector. He replaces Inspector Curry from the original novel. Here he has a hobby of being an amateur conjurer. When Miss Marple sees him with his magician's suitcase, she asks him how they make a person appears to be at two places at the same time. He replies, "They do it with mirrors, ma'am." This gives her the idea of how the crime was committed.