Keeper of the Grail by Michael P. Spradlin
Tristan is an orphan who has been raised by monks after he was left on the step of the Abbey when he was a baby. No one knows who his parents were or why he was left there. When knights come to St. Alban's Abbey, Sir Thomas asks Tristan to be his squire. Tristan accepts and travels with the knights to the Holy Land. When the fortress of the city they are in is put under a seige, Sir Thomas gives Tristan the Holy Grail, the sacred cup believed to have magic powers. Tristan sneaks out of the city and starts on his journey to Scotland. On his way, he meets Robard Hode, one of the kings archers. Robard saves Tristan from bandits and they continue together on Tristan's quest. On his journey, Tristan meets many unlikely friends while he hurries to keep the Grail out of the hands of Saladin, the muslim leader, and others, such as Sir Hugh who has a strange intrest and dislike to Tristan.