At the opening of Tower Bridge in June 1894, a would-be-assassin, Anton Grunwalski, is arrested, but later dramatically rescued from police custody. Detective Inspector Arnold Box, working with Colonel Kershaw, Head of Secret Intelligence, uncovers a conspiracy, the Aquila Project, which aims to assassinate the Tsar and plunge Europe into War. Venessa Drake, Kershaw's agent, poses as a maid in the household of the enigmatic Baron Augustyniak, where she learns that Grunwalski is on his way to Russia. Box and Kershaw pursue Grunwalski across Europe. In Poland, as an unwilling guest of Augustyniak, Box suddenly realizes the true purpose of the Aquila Project. After a desperate race against time, he and Kershaw bring their mission to a breath-taking conclusion.