Spring 1914. At a masked ball, the Duke de Richleau has an intriguing meeting with a beautiful woman - an incident that was to lead to a series of desperate adventures with a Serbian; a secret; a terrorist society; then as a British secret agent at the Austrian Supreme Headquarters. The capers culminate in the Battle of the Marne – the operation that shattered Germany's chance of victory.

Through the violence, intrigue and hair's-breadth escapes, there runs alongside the story of a great love.