Waiting For Sunrise by William Boyd

A young English actor travels to prewar Vienna seeking therapy for a private affliction, but an intense affair and a false accusation force him to flee with clandestine help that later binds him to British intelligence. As war erupts, he is drawn into a web of espionage in London and across Europe, using his theatrical skills and newfound psychological techniques to infiltrate circles of deceit and unmask a traitor. Along the way, shifting loyalties, dangerous liaisons, and startling revelations about his own origins blur the line between performance and truth.

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