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. But she has her own ideas and follows her intuition closer to answers but even closer to danger.

Amelia goes undercover to search for clues at Clara's home, while 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 he must step in when her investigation turns fatal.

Determined to keep Amelia out of harm's way, Holmes sends her back to the relative safety of undercover work. While Holmes searches for answers about the missing jewels, Amelia learns that in this society, the most dangerous place for a lady may just be a debutante ball.

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.

The game is afoot! Having cracked the code of the Red Thread's communications network, Sherlock, Amelia, and their friends are 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.

At a grand debutante ball, Sherlock and Amelia face off against the exposed Red Thread syndicate, where revelations, betrayals, and gunfire await.