 When an unidentified man is found murdered near the scene of a warehouse fire, Scotland Yard s laboratory is unable to identify him. Inspector Lestrade and a police sergeant take a sample of mud from the dead man s shoes, and go to Baker Street to consult Sherlock Holmes. Since Holmes is out, they try to analyze the sample themselves, using Holmes s notes and equipment. As they are working, a man enters the flat, demands money, and tells them that he has planted a bomb that will go off somewhere in London at 6:00 PM that evening. When Holmes returns and learns the details from Lestrade, he and Doctor Watson realize that they have to move quickly.