The Changing Tide is the sequel to The Magic Land. The two older children, Katy and David, are absorbed in trying to establish their own lives without interference from their aunt. They are brought up short when Aunt Jo dies and Katy discovers she is pregnant. The full responsibility of looking after the family-including Mara, who is crippled from polio, Ethan and Elfrida the twins, and the baby, Seth-falls on David. He has to get them through the harsh northern winter and keep anyone from knowing that Katy is having an illegitimate child. As the children grow and change, so does the land around them when oil is discovered and the wilderness is invaded by seekers after the black gold.