Witchblaze - The Reflected City, #3

Gruesome rites. Whispers of witches. Arabella's past has caught up to her. Arabella finally feels like she belongs. She's settled into her role as the Bearer of St. Brigit's Arcana. She has family, friends, and a purpose. And assisting the Phantasm Bureau has brought her close to handsome viscount Trey Shield, a formidable magician in his own right. But then a prized racehorse is found butchered in a grisly and familiar rite.
A beloved cousin arrives unexpectedly, bringing bad news. Arabella's family secrets create a rift between her and Trey, one that is further complicated when his intended bride comes to town. As Arabella struggles to resolve her family affairs, she realizes that they are enmeshed in a plot that threatens all of Lumen. She has to put a stop to her foes' evil schemes before they destroy all that she holds dear.
This fantasy in a Regency-esque setting is perfect for fans of Georgette Heyer and magic!