Agate: Then and Now (Stones of Power #4)

Time travel.

For mages, it violates their number one rule: what the Mother has written, let no one unwrite. The Mother writes the destinies of the creatures on the world of Karishian. If her writings were undone, it is feared that Creation itself could be undone. The Dark Mage Morgorth takes this rule to heart, but there are others who do not.

Morgorth is about to claim a stone of power when it is stolen from him by a female mage he hasn't seen in decades. As they struggle for the stone, she activates it, and Morgorth is unwillingly plunged into another time and another place. It isn't long before he realizes what time he's found himself in and there are a few familiar faces.

Most notable is a much younger version of Aishe. His mate.

Living with a tribe who will be massacred, caring for a young lad who will become his mate, and fighting a battle against a mage who can travel from past to future at a whim—Morgorth's life has never been easy but now he must contend with the will of the Mother. Unable to change the future and the tragedies of Aishe's life, he must decide what his role in his mate's past will be, and ask himself one vital question: how does one defeat time?