Jim and Josie Miller are already pioneer children in Indiana, when the story opens. Their father has gone to California in the Gold Rush of '49. Aunt Maria finds them a burden and big brother Ben does his best to take care of them. They are all relieved when the letter from California comes and the plans for the long journey overland can be made. The story of that journey is the story of the Pioneer Twins. The covered wagons, the long, slow march of the caravan, the Indians, friendly and hostile, the camp-fires, the prairies, the buffalo.