The Dog It Was That Died is a 1952 detective novel by E.C.R. Lorac, the pen name of the British writer Edith Caroline Rivett. It is the thirty sixth in her long-running series featuring Chief Inspector MacDonald of Scotland Yard, one of the more conventional detectives of the Golden Age of Detective Fiction. It was published by the Collins Crime Club.
When Rodney Bretton, a lecturer in mathematics, is knocked down and killed by a lorry is it assumed to be a tragic accident. However the drowning of his daughter Wendy in her bath a couple of months later leads MacDonald to launch an investigation.