Nyall by Hazel Hunter

A salvage diver tries to walk a fine line between the sea and the sand.

When Caroline Parrish is rescued from the waters of medieval Scotland, she quickly realizes that she’s landed in the midst of an ancient feud. But what’s even more unsettling are the feelings that she has for her two gorgeous rescuers.
Nyall MacMar, the clan’s Captain of the Guard, understands immediately that another woman from the future has arrived on Caladh. But even as he wades with her and his best friend through the surf, he knows that they’ve violated a brittle truce that can’t stand another blow.
For his part, Commander Jamaran of the Finfolk, can barely release the unconscious woman once they’re on firm land. While he knows that she must be fated for his friend, Nyall, he can’t help but feel his carefully built reserve start to crumble when she’s in his arms.
As the three of them try to navigate their way through roiling emotions, as well as the politics of the bay, a man-eating shark patrols the waters and the shape-shifting Cait Sith draw ever closer.