If you've seen the movie version of this... I'd recommend that you forget you ever saw it! Hollywood didn't seem to have read the book (and if they did, they completely missed the point). I've never really cared for the title-- it doesn't fit in well with the book, and it usually makes my stomach churn (but it comes from a quote from Steppenwolf by Hermann Hesse, which I have not read). That aside, the book itself is much better than its title suggests, though it does have its problems.
Vivian is a young loupe-garou (werewolf) whose pack-family is divided. Her father, the pack leader, died in a fire some time ago, and it's taken some time for the group to recover as far as they have. Which isn't much, Vivian realizes. With so much going wrong at home, Vivian seeks other companions and becomes romantically interested in a human boy at school named Aiden. The rest of the pack members-- especially the Five, the young male werewolves that are Vivian's age-- are not happy about her choice. As her relationship with Aiden progresses, she longs to tell him that she's really a loupe-garou. When she does, he laughs at first, but when she shows him her true form, he (understandably) runs. Vivian wishes he could see how beautiful she knows herself to be, and is upset with him for making Vivian hate herself. By the end of the story, however, she's found the one who appreciates her for herself, and embraces her new role in the pack.
Overall, the book has a pretty good storyline, but I felt that a few of the elements detracted from the point it was trying to make. There's some mild innuendo and sexual content that was unneccessary, and a few darker themes run through the storyline as well, marring an otherwise excellent book.