Content Warning: The guide and source text contain references to and descriptions of domestic violence, rape, sexual assault, institutional abuse, violent murder, suicide, and self-harm.

Sixteen-year-old Sage Winters waits to take a bus to Willowbrook State School in Staten Island in New York City in December of 1971. Sage has just discovered that her twin sister, Rosemary, didn’t die six years ago as Sage was told, but has been a patient at Willowbrook. Now, Rosemary has gone missing. As Sage waits, she thinks of her friends Heather and Dawn’s stories about the serial killer Cropsey. She thinks of her boyfriend Noah’s infidelity—she caught him kissing another girl, which reminds her of her parents’ divorce and her estrangement from her father. Sage’s mother is dead, and she now lives with her abusive stepfather Alan. Sage passes some missing posters, wonders where those children are, and imagines their fear and sadness.

Staten Island has always been a kind of dumping ground. In the 19th century, it was a quarantine zone for people with contagious illness. It has housed institutions like the tuberculosis hospital, the Farm Colony poorhouse, the Willowbrook State School, and the Fresh Kills garbage dump where many of the locals work.