“An American Crime” (9 p.m., Showtime): “An American Crime” stars Ellen Page

“An American Crime” (9 p.m., Showtime): “An American Crime” stars Ellen Page in the dramatization of a tragedy that will still shock you 40 years after it happened. Adapted from real life, “An American Crime” takes an unflinching look at a gruesome exercise of human cruelty and complicity.

The setting is Indianapolis in 1965, where 16-year-old Sylvia Likens and her youngster sister Jennie are left by their parents in the temporary custody of Gertrude Baniszewski, a single mother of five who’s coming unwound.

As Gertrude inflicts her punishment on Sylvia in escalating ways, the film is terribly disturbing to watch. Its saving grace: the performance by Catherine Keener as a pathetic monster, and, even more remarkable, Ellen Page (“Juno”) in the role of the preyed-upon teen.