At the opening of Tower Bridge in June 1894, a would-be assassin, Anton Grunwalski, is arrested but is later dramatically rescued from police custody. Detective Inspector Arnold Box, working with Colonel Kershaw, Head of Secret Intelligence, uncovers a conspiracy—codenamed the Aquila Project—that aims to assassinate the Russian 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. As he pursues Grunwalski across Europe, 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.