Triple Six (The Lightkeepers #2‪)‬

Descended from an ancient race, Earth's few remaining Lightkeepers battle the forces of darkness that threaten humanityMiraculously healed from the injury she suffered in the line of duty, Detective Micki Dare and her partner, Zach Harris, are called to investigate a string of brutal—and baffling—home invasions.The impossible surrounds the case—contradictory accounts by eye witnesses, guard dogs that slumber through mayhem, and perps with strangely similar tattoos—all a mathematic combination of three sixes.Soon, Micki and Zach must face a terrifying truth: their foe is a familiar one—a dark entity they thought they'd beaten. More powerful than before, this time it's threatening those closest to Micki. Without a forbidden alliance between humans and light beings, Micki and Zach will be defenseless against this all-encompassing evil—too late to save the innocents, and with them, the future of the human race.