Hattie Big Sky by Kirby Larson is a novel that takes place beginning in 1917 and follows the adventures of a sixteen-year-old orphan for approximately one year, telling her story from her own perspective. Hattie lost both her parents by the time she was five and has been reliant on a series of relatives for shelter and care, never really knowing a home of her own. At the age of thirteen, she is taken in by her Uncle Holt, who is really a distant cousin, and his wife Ivy. From Aunt Ivy's perspective, Hattie is inconvenient and should be placed somewhere useful as soon as possible. She finally accomplishes her goal when a local boarding house requires help, and though Hattie is sixteen and only months from finishing school, Ivy doesn't care. Uncle Holt is more inclined to let Hattie decide her future. He is one of her few supporters. The other is Charlie Hawley, who became her friend at thirteen and remained so, even giving her the old tomcat she calls Mr. Whiskers. Before Hattie is forced to make a decision about Iantha's boarding house, Uncle Holt gives her a letter. The postmark is from Montana, so she knows it can't be from Charlie, who left two months earlier to fight in the war. Opening it, she finds two letters. One is from a woman named Perilee Johnson Mueller, who says she promised the enclosed letter would be sent to Hattie as requested by her uncle when he passed. She claims that if Hattie accepts, she and her husband Karl will help in any way they can. The second note is from Hattie's Uncle Chester - her mother's only brother. He tells her that he has thought of her often, and though a scoundrel for most of his life, he had just begun to settle down when he discovered the cough he had was going to kill him. Now, his property of 320 acres in Montana is hers if she wants it. She only has to meet the remaining homestead requirements in order to keep it. Hoping she has some of her mother's backbone, he tells her, she is welcome to the house, a horse named Plug and a cow named Violet,. He suggests she dress warm and bring a cat if she decides to take him up on his offer, which he sincerely hopes she will. Ivy is beside herself, but Hattie is excited and answers Perilee's letter with one line - "I will come".

The next eleven months are an account of Hattie's adventures as a homesteader or 'Honyocker' in Montana. She had no idea what to expect when she left Arlington, Iowa and boarded the train, but Hattie's life changed forever when she made the decision to go. Spurred on by a feeling of finally belonging somewhere, Hattie takes on the challenge of proving up her Uncle Chester's land claim by cultivating one eighth of the 320-acre property, setting 480 rods of fence and then paying the final fee of just under thirty eight dollars for the free land. She tackles the challenge despite her initial fears, learning how to do all of these tasks and many more besides. In letters to Charlie and Uncle Holt, she relates her exploits as she learns how to care for her livestock, deal with a harsh and unforgiving Montana winter, cook, bake, wash, quilt and become a part of a community in an area that is wild and untamed. She finds friendship, learns the meaning of community, and discovers more about herself in the process than she believed possible.