The Quicksilver Court (Rooks and Ruin #2)

Ryxander, Warden of Gloamingard, has failed. Unsealed by her blood, the Door hidden within the black tower has opened. Now, for the first time since the age of the Graces, demons walk the world.
 
As tensions grow between nations, all eyes-and daggers are set on Morgrain, fallen under the Demon of Discord's control. In an attempt to save her home from destruction, Ryx and the Rookery set out to find a powerful artifact. But powerful enemies are on the hunt and they're closing in fast.