When retired nurse Frannie Greene moves into a senior living apartment, she finds a compelling friendship with her new neighbor Katherine, only to discover that Katherine is married to the judge who Frannie believes is implicated in the death of her beloved granddaughter.

Observing the medication cart sparks Frannie's darkest imagination, and her desire for revenge combines with her medical expertise. In one dreadful, impulsive moment, she tampers with the medicine. However, the next day, someone is dead, and Frannie realizes the gravity of what she's done.

The police get involved, and suspicions gather around someone Frannie knows to be innocent. Wracked with remorse, Frannie's anxiety becomes unbearable. As she works to make it right, Frannie discovers that things are more complicated than they seem.

She's spent years aching for accountability from people in power. Is she the one who now needs to be held culpable? What really happened that night?