Faith in the mystical, unseen, or in a god figure is the novel’s foremost theme and central to protagonist Irene’s character development. The story begins when Irene is just eight years old and full of curiosity. She finds her way up a secret passage and discovers that she has a great-great-grandmother with magical abilities living in the tower above her. Irene witnesses Grandmother’s magic and the way she can manipulate the world around her, and she falls asleep in Grandmother’s bed, overwhelmed by love. When she wakes, she is in her own room, and she wonders if it was nothing more than illusion. Irene’s faith and courage are thus tested by her grandmother, who becomes a beacon of light, safety, and wisdom. These traits, along with her ability to use magic, frame Grandmother as a godlike figure, and it is implied that she and Irene are of the moon and stars. George MacDonald was a devout Christian and uses Irene’s journey to illustrate the nature of Christian faith.

Despite having firsthand knowledge of Grandmother, Irene experiences several moments of doubt, questioning first her grandmother’s existence and later her benevolence.