At the beginning of the book Beck goes on a peaceful mission with colleague Ahlberg in Motala. His other colleagues, meanwhile, are looking for a handbag thief who is making the parks of Stockholm unsafe. In the park where the latest robbery occurred, a child's body is discovered by two tramps shortly after the crime. The 9-year-old girl has been abused and strangled. Shortly thereafter, the same fate befalls another child. As Beck returns, the police investigation is already underway. The police are initially lacking in clues as the abduction of the second girl was only witnessed by a three-year-old boy. An elderly
exhibitionist is briefly detained, but is found to have nothing to do with the murders. Only a coincidence advances the investigation: Gunvald Larsson (making his first appearance in this novel) had a telephone call at the very beginning of the investigation with an elderly lady who complained about a man in an opposite flat, standing all day on his balcony, looking at the road, and playing with the children, among other strange behavior. After Martin Beck remembers this call; with difficulty the note written by Larsson is found and by a mixture of obstinate investigating and the coincidence that the caller had the common name
Andersson, the killer is found, just before he can attack a child again. == Characters ==