Consumed By Fire by Kaje Harper

Sometimes you have to fight fire with fire.

Darien’s ready for a quiet life— back to studying, sleeping with his ridiculously appealing necromancer, playing magical Fetch with his dog-familar. But breaking the demon portals was only a temporary solution, when there are sorcerers out there rebuilding them. Much as he’d like to shove the rest of the job on someone else, Darien’s not willing to see his world burn.
Silas is ready to turn the whole hunting-dark-sorcerers mess over to the Guild. Except he doesn’t trust his council members as far as he can throw them, the sorcerer Chicago has sent sets his teeth on edge, and if they get it wrong, Darien’s life is at risk. So with Grim at his side, and Pip encouraging Darien, they, Jasper, and Magda will take on one more hunt to find and stop the portal-builders.