Night Angel: 3 Beyond the Shadows by Brent Weeks.
Logan Gyre is king of Cenaria, a country under siege, with a threadbare army and little hope. He has one chance, a desperate gamble, but one that could destroy his kingdom.
In the north, the new Godking has a plan. If it comes to fruition, no one will have the power to stop him. Kylar Stern has no choice. To save his friends-and perhaps his enemies-he must accomplish the impossible: assassinate a goddess.