The Seeking (Monstrous Creatures) by Marlena Frank

Each Seeking, the magic that protects the town of Carra must be renewed, which means the children of the Exalted Family must go into hiding. Whether through disguise or bribe, through trusted friends or perfect hiding places, every child of the Priest family must avoid capture for the full day of The Seeking.

When things go wrong with the renewal, it’s up to seventeen-year-old Dahlia, the middle child of the Priest family, and her girlfriend, Bisa, to escape Carra and find the magical beings responsible for the protection. They must learn who would require such a cruel game every year and if the protection of the Gray People is really worth such a price.

What they will discover is far worse.