Creator/EllenPage and Catherine Keener star in this dramatization of the real-life story of Sylvia Likens and Gertrude Baniszewski. Sylvia and her sister are left for an extended stay at the home of Gertrude and her six children. Times are tough and the increasingly unstable Baniszewski snaps and begins taking out her anger on Sylvia, repeatedly abusing and eventually torturing her. Things get worse when her kids and others from the neighborhood join in.
!!This film provides examples of:

* AdultFear: The worst fear of every parent who left their child in the care of a friend's family.
* AffectionateNickname: Sylvia's father calls her "Cookie."
* BasedOnATrueStory
* ColdBloodedTorture
* CompositeCharacter: Patty Ryan is a composite of three real-life girls involved in the historical events - Darlene [=MacGuire=], Anna Siscoe and Judy Duke.
* CreepyCircusMusic: The end credits, where [[CreepyChildrenSinging a children's choir]] imitates the piping of a circus calliope.
* DisproportionateRetribution: Much of what happens to Sylvia falls under this.
* DyingDream: The scene of Sylvia's escape and reunion with her parents near the end.
* ForegoneConclusion: The fate of Sylvia.
* HopeSpot: Sylvia's DyingDream of escaping and reuniting with her parents. You know it won't last, but still.
** There's also a point where, after spending all of her time torturing Sylvia, Gertrude gently washes her and is able to interact with her calmly, indicating that she's got a grip again. She loses it as soon as the local church's priest speaks to her about suspicions that Paula is pregnant, causing her to start lashing out at Sylvia again.
* HowWeGotHere: The film opens with and switches back and forth to the court trial of Gertrude and the others.
* HistoricalVillainDowngrade: What Gertrude did to Sylvia in real life was even worse than what the movie shows. The same applies to Paula, whose portrayal in the film implies that she had some sympathy for Sylvia. The RealLife Paula felt the same about torturing Sylvia as her mother did.
* JustFollowingOrders: The excuse that many of the people involved with Sylvia's death give.
* KidsAreCruel: What Gertrude did was horrific enough, but that so many other kids would join in makes it even worse.
* MarkOfShame: Gertrude (and later Ricky, when Gertrude is unable to finish) burns "I'M A PROSTITUTE AND PROUD OF IT" on Sylvia's stomach with a hot needle.
* SlutShaming: Gertrude does this to Sylvia for allegedly flirting with a boy.
* TakeMeInstead: When Gertie is about to beat both Likens girls, Sylvia offers to take both beatings to spare her disabled sister.
* TeenPregnancy: Gertrude had her oldest daughter Paula at a young age, and Paula herself gets pregnant by her cheating boyfriend. Gertrude is unable to deal with the thought that Paula made the same mistake she did, leading her to blame poor Sylvia and ultimately torture her to death.
* TheSixties: A rather darker side thereof--less free love and more secrecy and lack of child protective services.
* TortureCellar: Where Sylvia is eventually kept.
* WhereAreTheyNowEpilogue: In the final scenes, Sylvia relates the fates of many of her tormentors.
* WoobieDestroyerOfWorlds: Gertrude is this initially as we see her fall apart from the stress but it becomes harder and harder to sympathize with her as her actions become more horrific.
* WouldHurtAChild
* YankTheDogsChain: There comes a point where we're lead to believe that Sylvia will escape and be reunited with her family. The audience knows this won't last.