Holmes' brother Mycroft is caught in an explosion when his club, the Diogenes, is blown up. The player, first as Doctor Watson and then as Sherlock Holmes, investigates the explosion and discovers that it was not a gas leak but a bomb which was the cause. This leads them to investigate a case of espionage and the strange death of an unidentified man. In this game, establishing the identity of the victim is as important as finding out who killed him. The intricate plot leads the player to a great number of locations over town and involves several subplots.