After the mysterious disappearance of a refugee girl, it comes to another crime in the snowy Vienna. The Eight-year-old Elsie is missing. While the parents act extremely suspicious, the ambitious interior minister uses the chance to use the act politically in his favor.

The police desperately searches for the bodies of the disappeared children. The nervousness in the city increases. The authorities are in the dark. Suspects are being randomly detained. The interior minister uses the helplessness to enforce his security act. At the same time he draws the public attention to a therapy center for sex offenders.

After finding the three children's corpses, the question arises: who is the third child? A necklace with an M on it is the only clue. The police are baffled. The pace of the serial killer leaves no time to breathe. To give a sense of security, the police starts to "clean up" the underworld. But the underworld isn't just sitting and waiting...

The interior minister takes drastic measures to achieve his political goals. To clarify the identity of the third dead child, he puts images with the portrait of the corpse all over the city. The atmosphere is heated. The interior minister declares the Case M for a public case. Meanwhile, the Romanian beggars go in search of the murderer.

Things escalate. More children disappear. The fear of the people and the pace of the perpetrator allow the interior minister to shake the democratic foundations. At the same time, the police are able to identify the perpetrator. A race between the police investigation, the underworld hunting for the murderer and the political interests begins.

The curfew imposed by the interior minister is accepted without resistance from the population. In this ghostly atmosphere, the police hunts the perpetrator. But the underworld is also not just standing still...