In fifteenth-century Constantinople, Prince Constantine saves the life of a broken-hearted girl. But the price of his valour is high.

John Grant is a young man on the edge of the world. His unique abilities carry him from his home in Scotland to the heart of the Byzantine Empire in search of a girl and the chance to fulfil a death-bed promise.

Lena has remained hidden from the men who have been searching for her for many years. When she's hunted down, at last she knows what she must do.

With an army amassing beyond the city's ancient walls, the fates of these three will intertwine. As the Siege of Constantinople reaches its climax, each must make a choice between head and heart, duty and destiny.