Maisie is a 12-year-old Makah/Piscataway girl who injures (you're never sure exactly what she does to it -- tear, sprain, etc.) her ACL, or anterior cruciate ligament. It's a common injury suffered by 100,000-200,000 people every year, many of them amateur sports participants, from ballet to soccer to basketball.
Maisie thinks she's an aspiring ballet dancer, and as such, it's quite a set back. Like many kids her age, she's anxious and irritable with her family on the journey to recovery and still has dreams of returning to ballet. But they're inherently unrealistic dreams -- she doesn't realize she won't be able to do the things she did before her injury for a very, very long time, if ever.
That impatience and unwillingness to change her expectations leads her to not always be honest about the pain she's still feeling, which leads a physical therapist to OK her for more strenuous activity. She goes on a hike with her parents and ...big set back.
Maisie is lucky it happens to her while she's still so young. She has an opportunity to change her life's direction, but it isn't easy for her to mourn, accept the loss and move on. I know seniors in high school who've suffered similar injuries (in soccer, not ballet) after receiving scholarships, and it's devasting to not only lose the sport they love, but the ability to pay for college, as well.
This was a quick read, and it demonstrates the crushing emotional blow a physical injury like an ACL tear can deliver to performance athletes.