City of Lies (The Poison Wars, Bk. 1)

Outwardly, Jovan is the quiet, forgettable friend of the Chancellor's charming, irresponsible Heir. In secret, he's a master of poison and chemicals, sworn to protect the Chancellor's family from treachery. When the Chancellor succumbs to an unknown poison and an army besieges 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.