Tranq zombies

                            Berlin 2028:
The drug hotspot Leopoldplatz has turned into a zombie land.
Stefan, the vet, is sitting on a bench in this park. He is having a great time seeing junkies who can barely stand on their feet like zombies. Their skin is black and sometimes so rotten and eaten away that you can see the tendons or down to the bones. This is caused by the drug Xylazine, known in the scene as Tranq.
How did the drug spread in a district of Berlin to such an extent that Tranq zombies are dying every day in 2028? Who is responsible for the fact that junkies are now walking around the city like zombies? 
Inspector Bensky investigates the drug milieu. He has to solve three gruesome murders of Tranq zombies and one of a dealer. They were murdered in a bestial manner and found dead in a bunker.