Wings and Shadowthief by May Sage — book slip

Jack, a half-hunter and half-immortal, finds himself in a precarious situation when he wakes up covered in blood in Russia, with no memory of how he got there.

His powers, which he has long ignored, are now controlling him, and he must seek the help of a witch to prevent becoming the very creature he hunts.

Gwen, a witch who knows the rules of the Institute, has had enough of Jack after their one-night stand, but when he turns up at her doorstep asking for help, she can't refuse.

As they navigate their complicated relationship, they must also deal with angry gods and vengeful witches.

Fifth in the After Darkness Falls series.