Semir and Alex want to relax and spend a weekend at the Nürburgring. The Ballad of Bob Mayer, an old childhood friend of Alex can win with a victory the DTM. However, Semir and Alex can not just enjoy the spectacle, but must determine the traces they lead directly into the racing world in a murder case. When Bob Mayer comes under suspicion, Alex is in a dilemma: if he does his duty, Bob Mayer will lose the race of his life. During the race weekend roll over the events and it starts a race to the death.
In celebration of the 40th anniversary with Bonraths it comes to a stop. Semir, Alex and her colleagues escape while nearly died. Soon it turns out that the fact is accounted of dealer Grundmann, which is the highway patrol together with the LKA investigators Markus Hofer on the track. But Grundmann makes himself not keep their hands dirty doing another one for him: a so-called 'Cleaner', which can be hired from the underworld to make evidence disappear, to eliminate witnesses and any kind of problems to solve. But who is the Cleaner? And when he will strike again? Semir and Alex follow his trail and need to realize that they were tricked. For the Cleaner is none other than Markus Hofer, whose job has at LKA allows him Grundmann indemnify the back for years. As Hofer blows up, it will be too dangerous for Grundmann. The arms dealer wants to get rid of him. This is a fatal incident. Hofer's young son dies in shooting range of a sniper. He even manages to escape. Henceforth, the heroes are dealing with a tricky opponent, they always two steps ahead and their blind revenge eventually drives him to extremes. At the end of a merciless hunting Semir and Alex can not prevent that this case ends in disaster, someone from the PAST-family must pay with his life in.
The PAST family is still in shock: A member of the autobahn police was killed in an attack. Semir and Alex do anything to catch the murderer Markus Hofer. But when they recorded a first track, the two will be wiped out by the new chief prosecutor Sander: You all are too emotionally involved to continue to work on the case can objectively. But that holds the two does not occur. On their own they trace it on - and can arrest Hofer. But out of prison he beats both a barter before: his freedom - against the lives of hundreds of people! For Hofer knows, he claimed that the attack plans of an internationally wanted terrorist, who is out again soon. The proposal falls Alex and Semir in a crisis of conscience: Should they get involved in this pact with the devil? Together with Hofer make Semir and Alex on the way to avoid the last minute the attack on a fully loaded Hockey Stadium. But then both partners must recognize that Hofer held the whole time the reins. And now Hofer is free again to take cruel revenge.
In a car chase Semir gets into a hell of flames on the site of a gas filling station. At the last moment the fireman Tommy Gernhard saves him in front of a huge explosion. The attractive squad leader is the new boyfriend of Susan, who is expecting a child by him. When Alex and Semir little later an art handler locate murdered, it is the same Tommy, who flees from the scene. He swears Susanne, not to be the murderer and asks her for help to find the real culprit. But Tommy is not as innocent as he claims. Alex and Semir cover up Susan's dedication to her friend, but come by themselves targeted by Attorney General Sander.
Susanne is attacked by three masked youths. She has seen the face of one of the suspects, which can be identified. But since all three are a minor, they remain at liberty until the beginning of the process. To prevent Susan's testimony in court, the young people start with an extremely treacherous mind game that makes the police look pretty helpless. Because with this kind of criminal, they had hitherto never do.
When Kevin, the friend of the young soccer young professionals Mehmet Özman, dies mysteriously, Alex and Semir are puzzled. Why Kevin had to die? Mehmet's father Ahmet wanted to prevent the relationship, so as not to destroy the career of his son? Or was it suicide because Kevin is not coped with the growing career pressure and the game of hide his sexual identity? What do Caro, who was hired as Kevin's alibi girlfriend? Soon, the case takes a surprising turn, during the investigation and Alex Semir lead further and further into the depths of professional football
When Alex Semir wants to pick to work, he met his partner takes on a masked intruder who can Alex reflected and escape. Despite an intensive search Semir remains disappeared, concern for him is great. Targeted by the investigation unit of the neighboring Dr. Wenger, a psychologist. Isabel Frings know from earlier and decided to feel it on the tooth. Alex and Jenny pursue different tracks as you suddenly can locate Semirs phone. There come across the dead body of an unknown man, who was shot with Semirs service weapon. The further investigate the police, the mysterious disappearance is Semirs...
For Alex, Semir, Jenny and Attorney General Sander the day had actually started well. But soon roll over the events: A killing spree begins on the highway and leads into a hostage situation at a restaurant on the outskirts of Cologne. Amok's after targeted at a restaurant guest: Isabel Frings. In a thrilling season finale all the storylines come together in this restaurant. About four different perspectives of the same events, we learn that the destinies of our heroes, and many others are connected to this day closely. And although the whole process takes only a few hours, the rampage for all participants will have an impact. If you survive him.