An aimless young man, Johnny, is sent prison. He entrusts his beloved dog, Evie, to the care of his former lover and best friend, Frank. When he gets out of prison, he has to face difficulties at home. Added to this, is the fact that he may have to give up Evie to Frank.
The Mazarin Stone, a famous jewel, acts as a magnet for crime. Holmes investigates the latest and perhaps most curious episode in its adventures.