It is 1919, and while the world celebrates the signing of the Treaty of Versailles, Holmes and Watson are called to a grisly discovery. 

A severed hand has been found on the bank of the Thames, a hand belonging to a soldier who supposedly died in the trenches two years previously. But the hand is fresh, and shows signs that it was recently amputated. So how has it ended up back in London two years after its owner was killed in France? 

Warned by Sherlock's brother Mycroft to cease their investigation, and only barely surviving an attack by a superhuman creature, Holmes and Watson begin to suspect a conspiracy at the very heart of the British government...