Night Of The Unicorn by Jenny Nimmo
There it was - a sky full of shooting stars. They sped through the black night winking and glistening, and although their voices were silent, Amber felt they were trying to tell her a secret. The following morning, Amber awakes to all sorts of discoveries. Hennie, her favourite hen, has vanished; a strange white horse has appeared at the animal sanctuary; and Luke Foster, the unhappy new boy at school, confides in Amber his impossible wish. But perhaps what Luke is looking for is not so far out of reach. For it suddenly seems that anything might happen...