In a time when the Roman Empire is dealing with wars and invasions, Hippolytus, a Christian priest from the town of Myra, is sent to Britain to be the tutor to Gini and Gordi. These two children and their parents have fled the dangerous shores of the Mediterranean for the safety of distant Britain. There he earns the nickname "Father Horse," a reputation for wisdom, and the respect of the children. This is disrupted by the arrival of some Roman soldiers and the theft of some very valuable jewels. Suspicion immediately falls on Father Horse both because he is a newcomer and, worse, a Christian. In order to save himself, Father Horse has to solve the mystery and keep the peace with the soldiers. Fortunately, he can count on some unexpected help.