On the day obstetric surgeon Saara turns 40, after architect husband Leo has shared an exuberant birthday bonk with her, she discovers a half-used packet of condoms in his guitar case: she’d like to know where the missing condoms went. The answer to that question is of course that he’s been having an affair with a student, Tuuli. It doesn’t take her long to identify Tuuli and discover that, in the evenings, she teaches a self-defense classes. She signs up for the class with a fake name, befriends her; seeing Tuuli showering after the first class, she’s appalled by the relative youthfulness of the woman’s body. She also moves out and starts living alone. Bit by bit, Saara worms her way into Tuuli’s life. Partly by coincidence, partly on purpose, the two develop a close relationship. At the same time she is planning the best way to revenge her husband and his lover.