Orphan of Destiny by Michael P. Spradlin
Tristan and his friends, Robard and Maryam, have made it to Calais, France. There, Maryam was captured by Sir Hugh, who wants the Holy Grail for himself. When the three escape, they return with Robard to his home in Sherwood forest. But when they arrive, they find the forest is under control of the evil Sheriff of Nottingham. Will they be able to bring the Grail safely to Rosslyn and free the forest from the Sheriff's rule?