Of Wings and Wolves - The Cain Chronicles, #6

Summer Gresham knows that she's different. After all, she's the only twenty-year-old coed that shapeshifts into a wolf. But her unique nature is a well-hidden secret, so she's baffled to be singled out for a prestigious internship. She's even more stunned when she discovers that the man who wants to hire her--Nash Adamson--specifically requested Summer...and he won't take no for an answer. Nash has more than a few secrets of his own.
Like Summer, he's different, too: a rebel angel in exile. Summer is the key to his freedom, and her warmth and beauty stirs something inside of him that's been sleeping for millennia. She almost makes him forget that he's imprisoned. Summer suddenly finds herself at the crux of an ancient war, and angels don't care how many mortals get caught in the crossfire. Torn between saving Summer and freeing himself, Nash has to choose what matters most: their love, or his freedom.