The Wishing Beast

What can it mean when the Doctor and Mel are drawn to an asteroid by a message from the strange, elderly Applewhite sisters? The travellers are promised that they will receive their dearest wishes when they enter the frozen forests of this benighted shard of a world. But the ghosts that haunt this place are desperate to warn the Doctor about the sisters' promises. Only the ghosts know the true nature of the legendary Wishing Beast.