The Wind and the Wild by Emily McCosh

No one finds Faerie unless they are lost.

Living on the edge of the enchanted woods, Niamh often loses herself among the trees in search of food. Though her body bears reminders of a night long ago when monstrous hounds broke from those lands, she has not since glimpsed the fair folk, nor heard a whisper of their lovely, treacherous songs.
Until she finds a litter of helpless fae kittens where the mortal trees end, and signs of the hounds begin appearing in her little village.
Seeking answers, Niamh discovers a long-abandoned library hiding just beyond the eternal trees—and comes face to face with one of the noble folk. This strange fae lord appears more interested in friendship than trapping Niamh within Faerie, but it soon becomes clear he is not only gravely injured, but desperate to remain undiscovered.

She cannot help but wonder if he, hiding among his dusty books, is the very reason the hounds have returned.