Folke Mellvig

Brothers Kaj and Tommy are spending their summer vacation with their cousins Peter and Marianne, who are the same age, at Kullen in Skåne, while their parents go to Italy. The young people become involved in a tangled spy plot where it is not entirely clear who is on the good side and who is on the bad side. Espionage, mysterious light signals, and strange code words suddenly become part of everyday life, as do wild chases in mine tunnels, kidnappings, and nighttime break-ins. It will be a summer vacation they will never forget.

While four men blow up a safe, a night watchman is accidentally killed. They get away with the loot. Ten years later, the stepson of the dead night watchman receives vital information.

The married detective couple John and Kajsa Hillman goes on a vacation to Holmfors mill where a friend of Kajsa's lives with her husband. When a young woman is found murdered it is clear that this is another case for the Hillmans.

A model is murdered at a famous fashion house and the Hillmans start to investigate. Kajsa Hillman is employed as a model and discovers that several people had motives to kill her.

When private eye John Hillman is on assignment in London his wife Kajsa visits the Army's riding school at Strömsholm, Sweden. She gets involved in the strange murder of the Blue Rider. Unknown to everyone at Strömsholm.

On a tourist trip abroad the passengers on the coach witness an assassination attempt on the President Hurkas. One of the tourists has evidence against the perpetrators, and is killed when the coach reaches Sweden. Another passenger observes how one of the perpetrators is picked up by a yellow car. She is kidnapped and locked up in a mental hospital.

A ghost called Vita Frun (White Lady) is accused of several murders. Detective Hillman is contacted to resolve the case.