A Breath of Frost — Alyxandra Harvey

Emma Day and her two cousins -- Gretchen and Penelope -- are uninterested in their debutante lives. All the boring balls, tiresome curtsying, and polite conversation about nothing at all leave much to be desired. Even the dangerously handsome Cormac Fairfax is too frustratingly enigmatic to woo Emma, despite the fact that she can't stop thinking about him.

But when debutantes start being murdered -- and Emma keeps finding the bodies -- their worlds are turned upside down. The girls discover their secret family lineage of witchcraft and their own new magical abilities, which they must now embrace in order to stop the chaos, even if that means risking their lives.