Cruel Castle by Bryony Pearce

They thought the island was the end. It was only the beginning. They thought the island was the end. It was only the beginning. Ben and Lizzie are in hiding, presumed dead after escaping the island. If they’re ever to return to their families, they need to bring Gold down. So they secretly join Grady in the castle. But as the doors slam shut and the series of deadly challenges between them and freedom are revealed, it looks like history is going to repeat itself… Read more.