Vicky's younger sister Suzy grows emotionally during the trip, from wanting to adopt a fawn near the beginning to her later swift and competent rendering of first aid when another child is injured, despite wrong-headed demands by nearby adults.

Early in the trip, at a Tennessee campground, Vicky meets Zachary Gray, who arrives with his parents in a luxuriously equipped tent trailer pulled by a brand new black station wagon.

Observing Zachary's paleness and shortness of breath during an interpretive hike in Mesa Verde, Vicky's father, a doctor, deduces that he has a history of rheumatic fever that has damaged his heart.

Although the chronology of Madeleine L'Engle's Austin family and Murry-O'Keefe books places the events of The Moon by Night decades later, the concerns of the narrative itself are very much of the Cold War era.

Vicky refers to fallout shelters, Duck and cover, and, indirectly, to the involvement of Oak Ridge, Tennessee in the Manhattan Project.

Beyond these, the major theme and conflict of the story is Vicky's adolescent struggle to establish her own identity as distinct from that of her family, reconciling her existing loyalties with her growing need for independence.

Yet at the end of the novel, despite her earlier ambivalence toward religion, Vicky makes her stand against Zachary's nihilism, and cries out the words of the psalm as she awaits rescue.

The novel is based on a real-life camping trip made in the spring of 1959[1] by Madeleine L'Engle and her family, the Franklins, during which she first had the idea for A Wrinkle in Time.

At one point in The Moon by Night, Suzy Austin makes a joke about "tessering", and Vicky's first person narrative identifies this comment as relating to the story of Meg and Charles Wallace Murry.

After the camping trip, the Austins spend approximately a year in New York City, during which they experience the events of The Young Unicorns, aided by recurring L'Engle character Canon Tallis.

The following summer, in A Ring of Endless Light, Vicky meets another major L'Engle character, Adam Eddington, and also renews her relationship with Zachary.