Trial of Fate by Michael P. Spradlin
Tristan miraculously survives the storm that threw him off of the ship he and his friends were traveling on. He wakes up on the beach, surrounded by warriors. They take him to their camp and Tristan finds out that they are Cathars running from the authorities. After Tristan is reunited with Robard and Maryam, they help the band of Cathars get safely to their fortress. Tristan falls in love with the leader, Celia, and is drawn to their fortress. There, Celia helps the three friends escape, only to be caught again by Sir Hugh in Calais. Sir Hugh knows Tristan has the Holy Grail and will do anything to get it. With the life of a friend hanging in the balance, will they get out of this mess alive to complete their mission?