Night of the Witch by Sara Raasch and Beth Revis

Fritzi is a witch. The lone survivor of a brutal attack on her coven, she's determined to find her only remaining family member and bring the hexenjägers--zealot witch hunters--to justice for the lives they ended. To do this, she will need to take down their leader, the merciless and enigmatic Kommandant Dieter Kirch.

Otto is a hexenjäger--but that's just his cover. Years ago, the hexenjägers burned his innocent mother alive, and he has been plotting his revenge against the people who tore apart his family ever since. And now the time has come for them to pay for what they've done.

When Fritzi and Otto are unexpectedly thrown together, neither is sure they can trust the other. The reluctant truce fueled by their common enemy takes them from the city at the heart of the hexenjägers' power to the wild and mysterious Black Forest. As old truths come to light and new dangers are revealed, Fritzi and Otto uncover a horrifying magical plot at the center of the hexenjäger attacks that leads back to Kommandant Kirch . . . but their own growing feelings for each other may be the most powerful magic of all.