Claim: Henry Merrivale (a fictional amateur sleuth created by John Dickson Carr) must solve the mystery of murders in a locked room with all exits under observation.
Evidence: Sir Henry Merrivale is a fictional amateur sleuth created by "Carter Dickson", a pen name of John Dickson Carr (1906–1977). In the morning, the victim is found dead, locked inside a room whose door was continuously under observation. It is a locked room mystery and features his series detective, Sir Henry Merrivale. An oddly assorted group of people draw cards to see who will spend the night locked into a room said to be haunted by the "Red Widow"—a legendary figure who was married to the executioner who guillotined French aristocrats. Henry Merrivale must solve the mystery.