It is July 1881, and a frantic mother comes to 221B Baker Street, begging Sherlock Holmes to find her son. A naval officer posted to HMS Dido, he was part of the Naval Brigade that joined the Natal Field Force to fight the Boers. But he did not return with his men, and is being denounced as a deserter.

So begins a twisting tale of assassination, diamond mines and military cover-ups. Can Holmes and Watson uncover the truth, a truth that threatens the very fabric of the British Empire?