Today's story is set in London in the early 1900s. Sherlock Holmes and Dr Watson are called to investigate the murder of Sir Henry Trevor, a wealthy businessman. The only clue at the scene of the crime is a knife with the initials "H.V." inscribed on the blade. Holmes and Watson track down the knife's owner, a man named Harry Vincent, who tells them that he was framed for the murder by a man named James Wargrave. Wargrave is a former employee of Trevor's who was recently fired.