On a cattle drive in the desert on the night before Cowboy Ned's birthday, his horse Andy goes in search of a birthday cake, which he thinks will make Ned's birthday complete.
Seventeen-year-old Mattie leaves her sister Ivy in Last Chance, California, and disguises herself as a boy in order to get a job with the Pony Express, finding adventure, facing danger, and falling in love.
During the summer of 1916 thirteen-year-old Fayette and her brother accompany their widowed mother on a mule trip into the California mountains, where she is to establish library outposts in isolated communities.