Holmes and Watson are consulted by Inspector Gregson of Scotland Yard to assist with the "finger murders", where young women have been murdered and one of their fingers has been removed. Holmes and Gregson see Sir George Fenwick at Pembroke House with an attractive woman, Lydia Marlowe. The couple leave and Fenwick is drugged and later wakes to find another murder has been committed and that the finger is in his pocket. He returns to Marlowe's flat where he meets Professor Moriarty, who blackmails him. The following day Fenwicke is found killed, clutching a matchbook from Pembroke House. After an attempt on Holmes's life by a hypnotised former soldier, Holmes and Watson visit the Mesmer Club, whose members are all interested in hypnotism. Marlowe also visits the club and lures Holmes back to her flat where she hypnotises him. Moriarty instructs the hypnotised Holmes to write a suicide note and leads him to the terrace in order that the detective should commit suicide. Watson and the police raid the flat and Holmes reveals that he was not hypnotised after all. As he is being arrested, Moriarty tries to jump to the building next door, but instead falls, apparently to his death.