sarusaihiryu

Hi, I'm looking for a short story or extract from a novel set in England a few years after Richard I's crusade. The main character is a high-strung teenage boy named Stephen, who is raised by his guardian to believe that he is the son of a soldier who died heroically on the walls of acre. Stephen is given a mission which terrifies him but which he manages to accomplish. His guardian's friend is amazed by his guardian's pronounced relief, and it is then revealed that Stephen's father was hanged on the walls of acre for cowardice. I can't remember the name of the author or the title or anything. If anyone knows which book I mean, please tell me. Thanks!