Lefevre, a French archaeologist, has arrived in Istanbul determined to uncover a lost Byzantine treasure. Yashim is commissioned to find out more about him. But when Lefevre's mutilated body is discovered outside the French embassy, it turns out that there is only one suspect: Yashim himself.

Once again, Yashim finds himself in a race against time to uncover the startling truth behind a shadowy secret society dedicated to the revival of the Byzantine Empire, caught in a deadly game deep beneath the city streets, a place where the stakes are high - and betrayal is death.