In the last year of the Second World War, Penny goes to stay with Aunt Meg in the North of England for Christmas. One night, on waking, she meets Quintilla, a Romano-British girl who had lived almost two thousand years ago. Quintilla has travelled into Penny's time to help her find the tree of life her father needs in order to recover from his battle fatigue. The Dragonstone, a large green gem Quintilla carries in a pouch will help. They set off on their quest with two Icelandic horses, Snorri and Glampi. Soon, Penny realises that Quintilla is on a secret quest of her own. They enter a different world and meet strange people from folk-tale and myth who are at the same time quite down-to earth. And through all the travelling the two girls uncover surprising things about themselves and the world around them.