The Treasure Box - Orson Scott Card

A reclusive millionaire's hasty marriage leads to chilling revelations in the renowned author's "enthrallingly entertaining" supernatural horror novel (Booklist).
Software engineer Quentin Fears was only 10 when his beloved sister died in a car accident. Since then, he withdrew from the world into books and machines. Though he's made millions with his software, he avoids companionship at all cost—until a rare outing to a party brings him face to face with his dream woman, Madeleine.
She's smart, beautiful, and as naive to the world's ways as he is. They marry in a matter of weeks. Their relationship seems perfect—until Quentin meets Madeleine's cantankerous, eccentric family.
At their rambling mansion in upstate New York, Quentin learns of an ancient family secret to which Madeleine holds the key. Only Quentin can stop her from unleashing an ageless malevolence that will rule the world. But to do so, he must do what seems impossible — step outside himself into the world he has avoided.