Spooky things start to happen when Anna and Elas discover a secret door that leads to hidden passageways within the castle walls. What will the sisters find? Packed with mystery and adventure Phantoms of Arendelle will keep fans guessing right to the last page. Believing Kristoff has taken the day off work, Olaf volunteers himself for the role of Official Substitute Ice Master and Deliverer, with the help of Sven! Will Kristoff be able to stop his friends in time? Follow the loveable pair and their trail of chaos, in Olaf & Sven on Thin Ice.