One Dark Window (King Shepherd #1)

Elspeth Spindle needs a monster – an ancient spirit she calls the Nightmare. Only he can help her survive in the kingdom shrouded in magical fog. He protects her. He keeps her secrets. He is locked in her head. Elspeth's... life changes when she meets Raven Yu – the king's nephew, captain of elite soldiers… A traitor acting behind the back of his powerful uncle. Together they intend to gather the twelve Cards of Providence – a powerful magical deck that could be the key to freeing the kingdom from the eerie fog and deadly plague. But the stakes are rising, and the Nightmare is slowly and inevitably taking over Elspeth's mind. And she has little time left to stop it... and save herself.