London 1909: Vernon Kell, head of counterintelligence at the war office, wants to set up a Secret Service, but to convince his political masters he needs proof of a threat. And to find that proof, he needs an agent he can trust who is smart, ruthless, and able to blend in with the hoi polloi.

As it happens, the man Kell needs is Wiggins. An ex-soldier with a talent for deduction perhaps second only to the Great Detective, Wiggins was a Baker Street Irregular, part of a gang of urchin investigators trained by Holmes himself.
Unfortunately, Wiggins "don't do official," but when his best friend, Bill, is killed by Russian anarchists, Wiggins realizes that accepting the role of secret agent could give him the cover he needs to pursue revenge against Bill's killers.

Tracking down the Russian gang responsible for the murder and assembling a motley network of allies and informants in the process, Wiggins begins to unravel a deadly international conspiracy.