A Web of Obsidian - The Obsidian Sisterhood, #1

At 69 years old and with two martial arts black belts to her name, Sister Monica Barrett has never been one to back down from a fight. But the one that just landed on the ragged front lawn of the women's shelter she runs may be more than she's equipped to handle. At first glance, the assailant in pursuit of a young woman seems like an all-too-familiar story. But this attacker has powers-he moves with uncanny speed, strikes with brutal accuracy, and isn't after the woman at all.
Instead, he wants what she has: a flat, black stone with a spider's web embedded in it. The instant Monica touches the stone, her world is turned upside down. Power surges through her and destroys her adversary-the kind of supernatural power that should belong only to the God she serves. A horrified Monica is determined to rid herself of the stone and whatever it holds, but with more attackers coming after her and the women she shelters, she needs to move fast. Can Monica find where the stone came from before it falls into the wrong hands? Will it be safe to return it to its rightful place? Or has a nun of a certain age just inadvertently become the keeper of a dark power no human should wield?