Heal by Jennifer Snyder

The Clock is ticking.

Zoe thought finding her brother would be the end of the supernatural nightmare she found herself in. She was wrong. After Jeremy takes a bite from a dangerous snake shifter and becomes infected with his potent venom, a race against time begins to save his life. One in which Zoe finds herself dragged even deeper into the world of supernaturals and shifters.
Kai knows his only hope in saving Jeremy and keeping Zoe safe from Dravus is to find a witch willing to cast a spell that would slow the venom in Jeremy’s system. There’s only one family of swamp witches powerful enough to perform a spell of such caliber, but getting them to agree to it will come at a cost. One Kai isn’t sure he’s willing to pay.