All The Evils - Pandora's Jar, #2

To spy for an Empress is dangerous, but to cross one might be fatal. And if the Empress falls... It seems Anastasia, ex-courtesan of Constantinople, is always in the wrong place at the wrong time. After cheating death in the provinces, she returns to her home city only to find her friend's new lover on death row, a Nordic adventurer intent on winning her hand in marriage, and a city about to explode into anarchy.
Caught up in the coils of the subtle and brilliant Empress Theodora, she agrees to become a spy for the Empire, but she could hardly have chosen a worse time. Popular feeling is rising against the Emperor Justinian and his wife, and for once the city's warring sports factions come together to demand change. When a rival claimant emerges to the throne of the eastern Roman Empire, Justinian and Theodora's very lives are at stake - together with the lives of thousands of ordinary citizens.
Including Anastasia's.