Hound suspects Professor Moriarty for the rising counterfeit money problem in London, but is unable to find any leads until a little girl comes asking Hound to help her find her father.

Professor Moriarty thinks he has found a weakness in Hound, his land lady Mrs. Hudson, and so sets about kidnapping her, but things don't go as he planned.

The Royal Navy asks Hound and Watson to help them recover a submarine stolen by Professor Moriarty.