Salt Kiss (Lyonesse, 1)

From TikTok sensation Sierra Simone comes the first in the Lyonesse series, a spin-off of her bestselling New Camelot books.
Tristan Thomas is lost. After leaving the army, the young former soldier is in limbo. Until, that is, he's hired by Mark Trevena, the owner of Lyonesse―DC's ultra-secret club―to be Mark's new bodyguard. He's drawn into Mark's dark, seductive world of power and desire, and slowly drawn to Mark himself, even though Mark is everything Tristan knows he shouldn't want: cruel and wicked and shamelessly amoral.
But protecting Mark isn't Tristan's only duty: soon, Mark asks him to guard his soon-to-be bride as she travels home from Ireland on Mark's yacht. Tristan is jealous―and hurt to learn that the object of his obsession is engaged―but the former soldier in him is made to obey orders, and he goes to fetch Mark's bride for him.
Isolde Laurence is nothing like Tristan expected, however. Young, quiet, and sharp, she's being pushed into this marriage by her family, and as the two travel back to America, Tristan finds himself fascinated with Isolde and the glimpses he gets of the lonely but determined woman behind her reserve. And the fascination is mutual: one night, while sailing under the cold stars, they share a searing kiss. From there, it's a fast fall into the forbidden for all three of them.