She marries him for revenge. He marries her for her serpent mark.
On the eve of her twentieth birthday, Sol is kidnapped by a barbarian. He wants her to use the magic she doesn't have to heal someone. She wants to avenge her mother by killing his chieftain.
Desperate to get close to their leader, she marries one of their warriors. Her husband vows to never bed her. She vows to win his favor.
When she's plunged into his city, she realizes the depth of his people's prejudices. They will never accept her if she doesn't become like them. Even then, it may not be enough to obtain the vengeance she craves.
Betrayer is an enemies-to-lovers fantasy romance with plenty of tension and steam. It's the first in a series, ending with a cliffhanger. Intended for mature listeners.