Lena Odenthal has to balance work and family: her aunt Niki, a retired prosecutor, sharp-tongued and assertive, arrives in Ludwigshafen for a visit. At the same time, Lena and Johanna Stern are dealing with the death of a nursing home resident who was killed by an insulin overdose. Mr. Herrweg was over 90, and at most there are obligations to inherit - who had a motive to kill him? The inspectors examine the residents of the home as well as the victim's past. While Johanna would like it if the friendly family doctor at the retirement home wasn't involved in the case, Lena strangely always has the impression that Niki is also secretly involved in the investigation.