Acacia.

The bestselling historical novelist turns to epic fantasy with a powerful story of treachery, murder and revenge...Ruling from the island of Acacia, the emperor of the Known World has inherited an apparent peace and prosperity won by his ancestors generations ago. He's an intelligent man, a widower who dotes on his four children and it is this devotion that obliges him to hide a terrible secret from them: that their prosperity rests on the dark realities of trafficking in drugs and human lives. A man of integrity, he hopes that he might bring an end to this vile trade, but powerful forces stand in his way. And then an assassin strikes, a lone killer sent by the Mein, an ancient foe long ago exiled to the frozen north. Now the Mein have returned to take revenge on their old enemy and begin a series of brutal surprise assaults on Acacia. Mortally wounded, the emperor puts into play a plan that will allow his children to escape, to fulfil their destinies. And so begins a quest to avenge a father's death and restore an empire - this time on the basis of universal freedom...