Vagabond (The Grail Quest, #2)

Thomas of Hookton, having survived the battle of Crécy, is sent by the king on a mission to discover more about his father's strange inheritance, which rumored to be connected to the Holy Grail. But he is not the only person pursuing it and his rivals will stop at nothing. Now the holder of great knowledge, he is in even greater danger, facing at last his enemy and cousin, the elusive Guy of Vexille.