The Eagle's Wing by B.M. Bower

From the time he could toddle, Rawley had been taught that he must not go near the west wing of the house or approach the brooding old man in the wheelchair. There had been vague hints that Grandfather King was not quite right in his mind; that a brooding melancholy held him, and that he would suffer no one but his servant near him. Now, after nearly thirty years of studied aloofness, his grandfather had summoned him.<P>So began the greatest adventure of his life...