In the Coming of Tomorrow by Bree Wolf

In this magical time-travel romance from USA Today bestselling author Bree Wolf, 18th century Yvaine finds herself transported back to medieval Scotland, where she is swept into an ancient legend, an all-consuming forbidden love, and a centuries-old feud threatening everyone she holds dear.

In the aftermath of inter-clan bloodshed, Yvaine and Caelen defy their birthright as enemies, seeking refuge with their followers on the enchanting Fey Isles to forge a new future. Their love, forged across battle lines, now faces the ultimate test. Yvaine grapples with a heart-wrenching decision: to stay with Caelen in this ancient realm, or return to the future and the family she remembers.
As leader, Caelen is haunted by the prospect of Yvaine’s departure and the looming threat of old adversaries who seek their destruction. Just when peace within their new haven seems possible, whispers of an imminent attack by those harboring ancient grudges threaten to shatter their dream.
With their existence on a knife-edge, an ally emerges from the mists of the isles, offering aid. But with time running out, Yvaine and Caelen must stand united to protect their people and their love. In a place where myth becomes reality, they confront the ultimate test: can their love withstand the shadows of the past, or will the sins of their ancestors doom them to repeat history?