Bargain with a Beast by Grace Goodwin

Adrian Davis thought getting on a real-life, ‘beam me up, Scotty’, transport pad was adventure enough. Visiting her mother—and the Atlan beast her mom had chosen as a mate—on another planet? Setting foot in an Atlan prison? Completely crazy.
Like totally, bat-shit, what-the-hell-was-she-doing-with-her-life crazy.
She was supposed to spend a few days wandering around with her twin sister, seeing the sights, expanding her horizons. The trip was supposed to be a much needed break from the hectic schedule she was keeping in school. She was only nineteen. She had plans. Finish college. Medical school. Husband. House. Two-point-five perfect kids and a golden retriever named Buddy.
All that changed with one roar of pain. She heard him. A beast. He was out of control, locked behind an impenetrable wall, alone. Suffering the agony of mating fever.
Ready to die. Forsaken.
Adrian can’t let him go. She will have to fight a centuries old system, warlords on another world, and the beast himself to get what she wants.
To save him.
To keep him for herself.