In Vienna's sewage system, workers discover a washed-up sports bag with body parts. Moser finds out at which point in Vienna's gigantic sewer network the bag must have ended up in the wastewater. A little later, a witness comes forward who has observed the exit of a man from an advertising pillar, through which one can descend into the canal system. Rex shows Moser the exact location of the body. A little later, a second bag is found, this time with the body of the body. Dr. Graf discovers a tattoo on his body that allows conclusions to be drawn about the identity of the stranger: Josef Hartmann, who was in prison for bank robbery. Moser suspects that Hartmann was involved in a bank robbery that had taken place shortly before. In order to confirm his suspicions, the cashier Erika Reichel is questioned again. The case takes a surprising turn when Mrs. Reichel confesses that her boyfriend and Hartmann knew each other...