Holmes and Watson board a passenger train bound from London to Edinburgh, to guard the Star of Rhodesia, an enormous diamond worth a fortune belonging to an elderly woman of wealth; but within the first hour of the trip, the woman's son is murdered and the diamond stolen and any of the passengers in their car could be the killer thief.
A convicted thief in Dartmoor prison hides the location of the stolen Bank of England printing plates inside three music boxes. When the innocent purchasers of the boxes start to be murdered, Holmes and Watson investigate.
A mystery writer is intrigued by the tale of notorious criminal Dimitrios Makropolous, whose dead body was found washed up on the shore in Istanbul. He decides to follow the career of Dimitrios around Europe, in order to learn more about the man. Along the way he is joined by the mysterious Mr. Peters, who has his own motivation.
