Crusade. Keith Murphy Urban Fantasy Thrillers, #3

Keith followed orders: He came back home, freed his soul, and laid claim to a magic sword he never wanted to weild. All he wants now is the opportunity to walk away from his old life and forget the years spent killing things that go bump in the night. But Keith Murphy doesn't have time to rest, because his sorcerous partner Danny Roark is out of commission and the end of the world is thundering towards humanity like a freight train on steroids.
As the elder entities from the depths of the Gloom break through the veil of reality with increasing regularity, Keith's forced to assemble a rag-tag army of demons, seers, and reluctant allies to stop Ragnarök from occurring.