My Secret Unicorn Friends Forever by Linda Chapman

Most of the time Twilight looks like an ordinary grey pony but when Lauren says the words of a spell he transforms into a magical unicorn and together they can fly all over the world . . . Best friends Lauren and Mel are really excited about going to pony camp but when they get there they are surprised to find that theyre not in the same cabin. Mel soon makes lots of new friends and Lauren feels left out. But then she discovers that Mels teammates are not as nice as they seem. Can Twilights mag Paperback softback