Midnight Witch by A.D. Starrling

How do you defeat an enemy you cannot see?
After returning from Prague, a strange attack by hellbeasts leaves Mae Jin and her allies puzzled. Their suspicion that the Dark Council is behind the incident is roused when a reception attended by Mae, Nikolai Stanisic, and Vlad Vissarion takes a dark turn.
But it isn’t until Mae unwittingly triggers an unknown spell in a haunted church that she realizes the full extent of their foe’s plans. Overnight, the memories of almost everyone she knows are wiped out by the enemy’s sorcery and the magical realm turns against her, making her the country’s most wanted fugitive.
With the assistance of an unexpected ally, Mae, Nikolai, Vlad, and those of her friends immune to the trickery track down those who possess knowledge of the rare magic she unleashed.
With only two days left to foil the Dark Council’s sinister scheme, will Mae and Nikolai be able to reverse the spell before it’s too late?