Geum-ja Lee (Lee Yeong-ae) is released from prison after serving 13 years for a child murder she was forced into confessing to by the real murderer.

In preson she has recruited various cellmates to help with aspects of her plan to take revenge on the murderer - a teacher who she was having an affair with.

Her baby had been given for adoption when she was convicted and she also seeks to find her.

The two strands inevitably intermix and as the plot thickens the colour is gradually drained. Revenge becomes something darker, and reconcilliation is not easy.

Spoilers:

The murderer turns out to be a serial killer and Geum-ja recruits the parents of the other victims to decide how to deal with him after she has captured him - they agree to collectively slaughter him.