The year is 1897. Sherlock Holmes and Lucy James, his lovely young American daughter, must finally unmask the traitor who has crossed swords with them in their three previous adventures. Their secret adversary is now masterminding a well-orchestrated conspiracy to destroy the most glamorous event of the Century: Queen Victoria’s Diamond Jubilee Celebration. Lucy's growing relationship with Detective Constable Jack Kelly will be seriously tested as she and Jack work with Sherlock and Watson to defeat their murderous enemy. If they fail, the Queen and thousands of innocent people will die, and the British Empire will fall into chaos.