Just before Christmas 1908, Marion Gilchrist, a wealthy 82-year-old spinster, was found bludgeoned to death in her Glasgow home. A valuable diamond brooch was missing, and police soon focused on a suspect - Oscar Slater, a Jewish immigrant rumored to have a disreputable character. Slater had an alibi but was nonetheless convicted and sentenced to death, later commuted to life imprisonment in the notorious Peterhead Prison. Seventeen years later, a convict named William Gordon was released from Peterhead. Concealed in a false tooth was a message addressed to the only man Slater thought could help him - Arthur Conan Doyle. Always a champion of the downtrodden, Conan Doyle turned his formidable talents to freeing Slater, deploying a forensic mind worthy of Sherlock Holmes. Drawing from original sources including Oscar Slater's prison letters, this is Margalit Fox's vivid account.