One Monday morning in April, a middle-aged writer walks into her living room to water the plants and finds a woman standing beside her potted fig tree. Dressed in a navy blue trench coat and white Nikes, the woman introduces herself as "Mary. Mother of God.... You know. Mary." Instead of a golden robe or a crown, she arrives bearing a practical wheeled suitcase. Weary after two thousand years of adoration and petition, Mary is looking for a little...