The Prince and the Pilgrim — Mary Stewart

Eager, burning, and young, Alexander sets off towards Camelot to seek justice from King Arthur for the murder of his father. But he is diverted from his quest by beautiful, sensual Morgan le Fay, who persuades the young prince to attempt a theft of the Holy Grail....

Alice has lived a life of lively adventure, accompanying her father, a royal duke, on his yearly pilgrimage. Now she has come under the protection of a young prince whose brothers were murdered, a prince who is in possession of an enchanted silver cup believed to be the mysterious Holy Grail.

And so the stage is set for two young seekers to meet--and find the greatest treasure of all....