Chief Detective Bernd Flemming, Inspector Mariam Koch and Chief Inspector Max Ballauf have their hands full while the carnival is in full swing in Düsseldorf.

Two men break into the Düsseldorf building authority with the help of an employee. When they are surprised by the security guard while taking photos of site plans, they kill him and fake a robbery and murder.

A baffling discovery shakes Ludwigshafen: on the misty banks of the Rhine, a mother and daughter discover the body of a young man - yet when the police arrive, the deceased has vanished. Inspector Lena Odenthal faces a mysterious case, for the man presumed dead had only recently crossed her path as a witness in a drug investigation. As she picks up the trail of a mysterious figure known as "Mother," she has no idea that she is thereby putting her own life at risk…