Cursed Tides. Daughter of Air, #1

She no longer wants to be a part of his world. But he must convince her to save it.Ashe is one mission away from earning her soul. Nearly three centuries after her disastrous on-land escapade, the former mermaid has a final assignment: protect a marine biologist on his quest to save the oceans. Perhaps it's pure coincidence that Varun Zale is the descendant of the prince she once chose not to kill.
Varun can't explain how storms obey Ashe or why her eye color changes to match the tossing waves, but he suspects she is more than the mute ship captain she pretends to be. His growing fascination leads him from the shallows of a fairy tale to the depths of a mystery older than recorded time. In the midnight reaches of the ocean, monstrous titans stir. An unstoppable disease becomes a weapon in the hands of the mer-king.
Nothing Varun has ever imagined or believed about mermaids is true. And being wrong could cost him everything.