When her nurseryman father's favorite new flower, Blue Mystery, disappears, Annegret determines to find it and the person who took it. Solving the mystery takes her beyond the security and comfort of her home out into the German town where she lives. Here, for the first time, she sees and understands that others do not have her privilege. Annegret's moral dilemmas give substance to the charm of this mystery that, at the time of its publication, showed Germans, so recently enemies of the United States, as human beings.

A mystery story set in a German town: Who had stolen the priceless blue gloxinia? How had it been taken from the experimental greenhouse? Many people coveted the plant, perhaps enough to resort to stealing, but only an employee of the nursery would have had access to it. The evidence pointed strongly to the young red-haired apprentice, Fridolin. Aloof and sullen, he did little to defend himself. But ten-year-old Annegret, daughter of the nursery owner, was not convinced of his guilt.