Beauty and the Shapeshifter by Melody Raven

When Ella's father is missing, she finds him held captive by a dangerous and devastatingly handsome a man, who gives her one choice: Her father may go free, but she must stay with him--for good. 

There is more to Lucian than what Ella initially sees. He isn't just a crazed kidnapper wrapped into irresistible eye candy. Heading a group of shape shifters who live as humans by day and hideous monsters by night, Lucian is desperate to uncover why his kind hasn't been reproduced in centuries. Determined to solve this mystery, Lucian sees Ella as an answer. Together, they begin to discover the truth--a truth that just might be what Lucian's been afraid of all along. 

But their days together are numbered. Lucian's enemies will stop at nothing to destroy him--and anything he loves. Lucian and Ella refuse to give up that easily. Will beauty and love prevail, taming the beast once and for all?