Kian by Grace Brennan

Jessica Matthews is hiding a big secret. A couple of them, actually. The first is the alpha of the War Cats tribe is her mate, but she can never claim him. She’s one of a kind—a submissive tiger. The alpha needs a warrior for a mate, not a shrinking violet. And the other secret… well, she isn’t sure. Something strange is happening to her. Something she doesn’t understand. Something that’s changing her into someone she doesn’t know. And it terrifies her.
Kian Mannan is a true warrior. He has inherited a tribe he never really wanted, changing them for the better, and survived multiple attempts on his life. But his downfall is going to be one gorgeous War Cat he’s known was his mate for years—Jessica Matthews. He can’t claim her—yet. Not until Durga Valley is a safe place. But waiting is killing him slowly. He needs his mate by his side, now.
Kian is on a race against time, trying to protect Jessica from his tribe members, and Drako, the mysterious stranger who appeared out of nowhere. He’s fighting battles that are getting him no closer to winning the war, when all he wants to do is take Jessica and run. But Kian soon realizes that the greatest threat to Jessica might be herself, and that is the one person he can’t defeat. He must decide to take on his greatest battle, even when the whole world is crashing down upon him, or let her go and put his duty before his heart.