On a foggy night during the London Blitz, a special constable arrests a young Canadian soldier standing over the dead body of his elderly great uncle in a rundown house in Hampstead. The only other possible suspects are the inhabitants of the art studio next door, a celebrated painter, his sister and their various guests. However as MacDonald and his assistant Inspector Reeves begin to investigate a number of other possible suspects and motives emerge, including the special constable himself.