Released by Universal Pictures, it is the last of fourteen films starring Basil Rathbone as Sherlock Holmes and Nigel Bruce as Doctor Watson.

[3][4] John Davidson, a convicted thief in Dartmoor prison, embeds code revealing the hidden location of extremely valuable stolen Bank of England currency printing plates in the melody notes of three music boxes that he crafts to be sold at auction.

While confronting her, Holmes is ambushed by her accomplices, handcuffed, taken to a warehouse, hung by a rafter, and left with poison gas filling the room.

Holmes manages to make it back in one piece and, while conversing with him, Watson offhandedly mentions a quote from Dr. Samuel Johnson.

Having stolen all the boxes and deciphered their message, Courtney and gang join a tour group at Dr. Samuel Johnson's house, now a museum, where they slip away and find the plates hidden within a bookshelf.