Blackmailed and sidelined from investigating, Sherlock Holmes finds hope when a young woman arrives on his doorstep, potentially holding the key to solving the kidnapping of an ambassador's daughter.

While Sherlock chases a stolen carriage, he sends Amelia on a hunt across London; Amelia has her own ideas and follows her intuition closer to answers but even closer to danger.

Amelia goes under cover to search for clues at Clara's home; Sherlock goes to prison under pretense of meeting his forever foe, Moriarty.

Amelia withholds details from Holmes after encountering a charming man with a pistol, but Sherlock must step in when her investigation turns fatal.

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 cracked the code of the Red Thread's communications network, Sherlock is hot on the path of the kidnap victims, chasing a trail of breadcrumbs that leads all the way to the vaults of the Bank of England.