His Star Princess by Finley Brown

Desire draws her closer to him with the seduction of his control. Proclaimed the Celtic princess at birth, Fianna was born with all the knowledge of the stars and the moon. Able to read the night sky as a map, she can also discern the stars’ meaning and, with them, the future. So, when she is asked to help navigate a secret mission to the new world, she leaves her beloved Scotland for the first time. Only, the journey proves to be perilous, and Fia is teamed up with a Knight Templar whose life is governed by rules and strict obedience. From the beginning, he demands her submission.
James Davidson has one chance to prove himself to the secret society, The Ring of Priests, and it requires him retrieving a hidden artifact. Things become complicated when the princess, who is under his protection, is abducted and he must face the secrets of his past to find the real treasure.