McGuire, Seanan. InCryptid novel.

DAW book collectors #1752

"As the youngest of the three Price children, Antimony is used to people not expecting much from her. Annie's expectations keep getting shattered. She didn't expect Verity to declare war on the Covenant of St. George on live television. She didn't expect the Covenant to take her sister's threat seriously. And she definitely didn't expect to be packed off to London to infiltrate the Covenant from the inside...--Publisher's description