The Midwinter Hunt. Leland Sisters, #5

Persy Leland and her twin sister, Pen, are thrilled to be invited to the season's most coveted event: the Midwinter foxhunt at their neighbor's estate. Their horse-mad little brother Charles, however, is forbidden to join them- he's too young, too reckless, too eager for adventure. While searching for a place where he might at least glimpse the hunt's start, Persy discovers a small fox, ensnared by a strange enchantment in a silent winter field, and smuggles it home to nurse it back to health.
But her act of kindness stirs up something older than winter itself. The next morning, a shadowed huntsman rides out of the mist-his smile sharp as moonlight, his gaze fixed on Charles. Now Persy and Pen must protect their brother and the enchanted creature they saved before the Midwinter hunt claims them all.