Having survived their first time-slip adventure (A Chase in Time), Alex and his sister, Ruby, have tumbled back through the mirror into the freezing-cold winter of 1947. Food is scarce in the aftermath of the Second World War and life at Applecott House is hard. The children decide to solve the mystery of a missing family heirloom, little expecting to find themselves trekking across the snow and having an adventure involving a frozen waterfall...