The three Musgrave siblings - Geoffrey, Philip and Sally - have opened the doors of their family estate, Musgrave Hall, to convalescing military officers during World War II. As his contribution to the war effort, Dr. Watson has been donating his services and treating several of the men there, some of whom are suffering from shell shock and as a result behave oddly. When one of Watson's colleagues, Dr. Sexton, receives a knock on the head, Watson asks his good friend Sherlock Holmes to investigate. Just as they arrive, they find Geoffrey Musgrave dead. Soon after, Philip is also killed and Holmes is convinced that it's somehow related to a poem the next heir to the family estate must recite when someone dies. Known as the Musgrave Ritual, it is a long poem that is gibberish to most but the great detective is convinced it holds the clue to solving the murders.