A group of young people gathered on the countryside to celebrate midsummer. On the journey home the car some of the youngsters are traveling in collides with a bus.
A 19-year-old boy, after his mother's death, starts a relationship with his father's mistress, although he is engaged. The relationship continues after the woman has become his stepmother.
A dead and unknown woman, is found in a canal. Police inspector Martin Beck becomes involved in the case. After several months the woman is identified. The police reconstruct the woman's last trip on the canal boat "Wilhelm Tham".