The Testament of Sherlock Holmes is an entry in the long-running Frogwares adventure series about the fictional detective created by Arthur Conan Doyle. The game has no ties to any of the previous games and presents an original story not based on the writer's works. It is set in London, 1898, after Holmes just solved a case where precious jewels were stolen. Upon returning it however, the necklace turns out to be a fake and the detective himself becomes incriminated. On top of that, when he has an appointment with the Bishop of Knightsbridge and arrives there, the bishop is tied up and mutilated. While the player initially controls Sherlock Holmes, his strange behavior eventually will have the player control his fellow partner Watson, who needs to investigate himself whether Holmes is really implicated.