A Royal scandal, a dazzling game of cat and mouse. The seductive Irene Adler is cold, calculating, brilliant. Has Sherlock finally met his match?
The team discovers a sleeper agent with terrifying connections in the US military. Faced with a formidable foe who not only appears to be a traitor, but a trained spy with access to US bases, MI5 may be out of its league.
Sandy and Jeanne continue to clash, and a possible asset claims to have important information about a communications breach.
While investigating the murders of several low-level criminals, the team discovers that the serial killer nightmares Sgt Fredo's daughter has been having are in fact connected.