Twelve Nights

Kay's father has gone missing on Christmas Eve! And when Kay and her sister Ell go to his office, everyone he works with claims never to have heard of him. So
later that evening, when Kay wakes up to find two mysterious strangers outside her bedroom window, talking about her father and looking for the last remnants
of his existence, she demands to know what's happened to her dad.

The two strangers, Flip and Will, are wraiths, on a mission to bring Kay and Ell's father to their world-the world...