A Man Lay Dead is a detective novel by Ngaio Marsh; it is the first novel to feature Roderick Alleyn, and was first published in 1934. The plot concerns a murder committed during a detective game of murder at a weekend party in a country house. Although there is a side-plot focused on Russians, ancient weapons, and secret societies, the murder itself concerns a small group of guests at Sir Hubert Handesley's estate. The guests include Sir Hubert's niece (Angela North), Charles Rankin (a 46- or 47-year-old man about town), Nigel Bathgate (Charles's cousin and a gossip reporter), Rosamund Grant, and Mr and Mrs Arthur Wilde. Also in attendance are an art expert and a Russian butler. Unlike later novels, this novel is more focused on Nigel Bathgate and less so on Alleyn.
During the detective game of murder, one of the guests is secretly selected to be the murderer, with a victim of his own choosing. At the time of the murderer's choice, he taps the victim on the shoulder, indicating that "You're the corpse". At that point, the lights go out, a gong rings, and then everyone assesmbles to determine who did it. It is all intended to be light-hearted fun, except that the corpse is for real.
This novel was adapted for the television series The Inspector Alleyn Mysteries, with the most notable change being that the Angela North character was replaced by Agatha Troy, who appears in later novels as Alleyn's romantic interest.