"Years later, after she had grown to a woman and begun to have children of her own, Caroline was to ask the Doctor how he had been so clever as to know that she would want a key to the library. The Doctor explained: ‘As a little boy, I lost my own father, who, like your royal highness’s, was a well-read man; but later I came to know him, and to feel his presence in my life, by reading the books he left behind.’ "