The 4 season of Rentnercops was broadcast on Das Erste from mercredi 8 janvier 2020 to mercredi 22 avril 2020. It consists of 16 episodes, the first one is called "Fossi" and the last one "Die lieben Kollegen".
In Cologne-Mühlheim, young police officers are not available. Commissioner Hui Ko holds the position with the ambitious Head of Department Vicky Adam, but otherwise there is no one available far and wide who wants to do the job. When a corpse in a carnival uniform is dug up in the city forest, police chief Plocher comes up with the idea of bringing back the two commissioners Edwin Bremer and Günter Hoffmann, who worked on the case 18 years ago. For the two reactivated commissioners, who have 40 years of service between them, the change is just right. While Günther is now being kept busy as a full-time grandfather by his grandchildren, Edwin mourns his late wife and is lost in self-pity and neglect.