Don't mess with Sander! Rumors are swirling: Is Fritz Schniedewitz really stepping back and selling his Aachen detective agency to the highest bidder? While Britta Sander and her colleagues try to solve this highly personal mystery, the enigmatic art and antiques dealer Tom Hartwig approaches them with a request. One of his closest associates has been brutally murdered, and Hartwig - a man with a dark past - wants no police involvement. Ignoring all warnings, Britta takes on the case, the true nature of which her partner, Chief Detective Körber, must never find out. As she searches for the brutal murderer, she becomes increasingly entangled in the dangerous world of the charismatic Tom Hartwig, until her own life is ultimately in grave danger.