Her Wicked Scot. The Highland Warrior Chronicles, #4

A warrior rumored to have no heart... Sent into Pictland to discover the identity of a desperate assassin, Ewan MacKinnon fights his fascination with the aloof princess, Briana. Although he wants nothing more than to take her into his arms, he won't taint her with the curse that has blighted him all his life. An ice princess, who has vowed never to love again... After her first disastrous marriage, Briana is determined to dedicate her life in service to Pictland and her beloved goddess.
But her goddess is elusive, sending only visions of a splintered future--a future that is tied irrevocably to the one man she fears could shatter her heart forever. The enemy of her people, Scots warrior Ewan MacKinnon. A forced marriage that could break them both... As Briana and Ewan battle both duty and desire, political intrigue tightens its noose around them. But with the assassin edging ever closer they must forsake the shackles of their past and risk their fragile love for a chance of surviving an ultimate betrayal.