Crimson Shore by Brenda Rothert

Power. Betrayal. A love that could save them all—or destroy everything.

Briar Hollis made her choice, but Blue Arrow Island doesn’t forgive. It doesn’t forget. And it sure as hell doesn’t let you leave unscathed. The war for control of the brutal island is escalating, and now that Briar has allies at her side, the stakes have never been higher.
A new player has entered the game.
When a new prisoner arrives on the island’s blood-soaked shores, the fragile balance of power shatters. The rules have changed. Survival now demands impossible choices. Briar is still learning to wield the power the island gifted her—but time is running out.
He shattered her heart. Now she’s all that stands between him and oblivion.
The war between the island’s ruthless leaders has turned personal, and Briar stands at the center of a storm whose destruction won’t end at the shore. The man who destroyed her—whose lies cut deeper than any blade—harbors a power so volatile it could consume everything. But it’s killing him from the inside out.
To defeat the darkness rising from the island’s depths, Briar must do the impossible: trust the beautiful, broken man who taught her that love and betrayal are two sides of the same coin.