The Man in Black by Stanley J. Weyman

It is a pleasant thing to be warmly clad and to lie softly, and at night to be in shelter and in the day to eat and drink. But all these things may be dearly bought, and so the boy Jehan de Bault soon found. He was no longer beaten, chained, or starved; he lay in a truckle bed instead of a stable; the work he had to do was of the lightest. But he paid for all in fears -- in an ever-present, abiding, mastering fear of the man behind whom he rode: who never scolded, never rated, nor even struck him, but whose lightest word -- and much more, his long silences -- filled the lad with dread and awe unspeakable. Something sinister in the man's face, all found; but to Jehan, who never doubted his dark powers, and who shrank from his eye, and flinched at his voice, and cowered when he spoke, there was a cold malevolence in the face, an evil knowledge, that made the boy's flesh creep and chained his soul with dread.

The astrologer saw this, and revelled in it, and went about to increase it after a fashion of his own. Hearing the boy, on an occasion when he had turned to him suddenly, ejaculate "_Oh, Dieu! _" he said, with a dreadful smile, "You should not say that! Do you know why?"