The 4½ friends have been assigned a real mission for the first time. Mr. Kozlowski, president of the Gardeners' Association, tasks them with spying on Mr. Ritter, his opponent in the upcoming elections. Kale and his friends keep a close eye on him.

Since he goes to the gym every day, there's nothing left to do but for them to work out as well – much to Friedel's dismay, who hates exercising. What is in the mysterious package that Mr. Ritter hands to two athletes? What is Mrs. Schulte-Stratmann, the Biology teacher, doing in a state of advanced pregnancy at the gym? And why does she particularly meet the man that the 4½ friends are spying on? The little detectives will put on tracksuits to participate in the most suspicious endurance training program and solve the mystery...