Murder by Decree is a 1979 British-Canadian mystery thriller film directed by Bob Clark. It features the Sherlock Holmes and Dr. John Watson characters created by Sir Arthur Conan Doyle, who are embroiled in the investigation surrounding the real-life 1888 Whitechapel murders committed by "Jack the Ripper". Christopher Plummer plays Holmes and James Mason plays Watson. Though it features a similar premise, it is notably different in tone and result to A Study in Terror. It is loosely based on The Ripper File by Elwyn Jones and John Lloyd.