Mist Warrior by Kathryn Loch

When he was twelve, Branan witnessed the man he knew as his father, Strickland, strike the blow that would kill his mother. Knowing she is dying, his mother tells Branan the of the secret she has kept since his birth. She tells him the truth of his heritage. Branan is the son of a Scottish Laird, Raulf MacTavish. Strickland murdered Branan’s true sire and forced his mother into marriage.
With the help of a foster family, Branan flees Inglewoo and finds safety with his father’s clan in Scotland. But Strickland’s abuse has created a black shadow in Branan’s soul, a rage so feral he cannot control it. He must walk a fine line, with one foot in the mists of darkness and the other in reality with only the illusion of control.
Twelve years later, Branan returns to Inglewood, now a skilled warrior and the day of reckoning shadows his steps. He is determined to seize his destiny and forever banish the black rage within him.
But upon his return he discovers his beloved foster family murdered and the woman he loves betrothed to another man, and without Catriona, the black demon within his soul rages more powerfully than ever..
He faces a battle that will decide much more than vengeance or even justice. If he falters he will lose himself to the black rage seething within him. Branan knows if that happens he will become as vicious as Strickland, a man he abhors.