Evan loves being big brother to Sam and Finn. They do everything together--go fishing, climb trees, and play astronauts. But lately, Evan notices that he and Sam don't look like brothers anymore. Sam wants to have long hair, and even asks to wear a dress on the first day of school. As time goes by, Evan comes to understand why Sam wants to look like a girl--because Sam is a girl. Sam is transgender. And just like always, Sam loves to dream with Evan and Finn about going to the moon together. Based on one family's real-life experiences, this heartwarming story of a girl named Sam and the brothers who love and support her will resonate with readers everywhere.