Sherlock searches for the missing jewels and their connection to the kidnapping of his friends; he turns to the insurance investigator, Birtwistle, for his assistance.

As Sherlock and Amelia identify the villains surrounding them on all sides, Holmes repays a favor to his oldest enemy, arranging a meeting between Professor Moriarty and the young Australian man who has suddenly become very close to Amelia.

Having unmasked the Red Thread syndicate, Sherlock and Amelia must confront their enemies at the most anticipated debutante ball of the season.