City of lies

"Outwardly, Jovan is the lifelong friend of the Chancellors charming, irresponsible Heir. Quiet. Forgettable. In secret, he's a master of poisons and chemicals, trained to protect the Chancellors family from treachery. When the Chancellor succumbs to an unknown poison and an army lays siege to the city, Jovan and his sister Kalina must protect the Heir and save their city-state. But treachery lurks in every corner, and the ancient spirits of the land are rising... and angry"--Amazon.com.