In Chapter One, nine-year-old Pippi Longstocking moves into an old house that her father—who is lost-at-sea and presumed dead by everyone but Pippi—bought years ago as a retirement home for himself and his daughter. Pippi's mother died when she was a baby, so her only housemates are a monkey named Mr. Nilsson and a horse that spends most of his time on the porch because, "he'd be in the way in the kitchen, and he doesn't like the parlor" (1.29). Obviously.
So you know, typical Chapter One stuff.
After we meet Pippi, Pippi meets her neighbors, Tommy and Annika Settergren, two "good, well brought up, and obedient children (1.10)"—not exactly the words one might use to describe Pippi. Free-spirited? Wild? A little bit crazy? Yeah, those suit her better. Needless to say, with Pippi in the fold, adventures ensue.
In the succeeding chapters, Ms. Longstocking, who also just happens to be the "strongest girl in the world" (7.55), takes on the local bully, some well meaning adults and police officers who want to put her in a children's home, a teacher, an ornery bull, a circus strongman, and a couple of burglars, to name a few. In every instance, Pippi comes out on top, as is her way, and while Tommy and Annika remain polite and obedient throughout, they clearly admire Pippi's style.
The book ends with Pippi, Annika, and Tommy (along with Mr. Nilsson and the horse) celebrating Pippi's tenth birthday, although Pippi's last line, "I'm going to be a pirate when I grow up! Are you?" suggests that Pippi, much like Peter Pan, will always remain young, high-spirited, and unconquerable.