Ragna Riegel works in a supermarket and still lives in her childhood home. She's alone in the world since her only son moved to Berlin. She longs for a Christmas or birthday card from him.

Ragna lives her life within strict self-imposed limits: she sits in the same seat on the bus every day, on her way to her predictable job. On her way home she always visits the same local shop. She feels safe in her routine, until one day she receives a letter with a threatening message scrawled in capital letters. An unknown enemy has entered her world and she must use all her means to defend herself.

When the worst happens, Inspector Konrad Sejer is called in to interrogate Ragna. Is this unassuming woman out of her depth, or is she hiding a dark secret?