The door in the wall (Yearling Books)

Ever since he can remember, Robin, son of Sir John de Bureford, has been told what is expected of him as the son of a nobleman. He must learn the ways of knighthood. But Robin's destiny is changed in one stroke: He falls ill and loses the use of his legs. Fearing a plague, his servants abandon him and Robin is left alone. A monk named Brother Luke rescues Robin and takes him to the hospice of St. Mark's where he is taught woodcarving and--much harder--patience and strength. Says Brother Luke, "Thou hast only to follow the wall far enough and there will be a door in it." Robin soon enough learns what Brother Luke means. And when the great castle of Lindsay is in danger, it is Robin, who cannot mount a horse and ride to battle, who saves the townspeople and discovers there is more than one way to serve his king..