The film is from 1973, it starts in one of the seedier parts of Berlin. Jürgen is Bernd Ziegenhals, a student, who has more or less given up on studying and tries instead to write books, which get rejected by the publishers. He shares a flat with an old man and the prostitute Mizi (Elke Sommer) and a toilet on the staircase with a lot more people. Mizi anounces, that she has now saved enough money and will give up her profession and move away soon.
In contrast we see his future opponent, the successful sociology professor Kolcyk, who lives in a villa in the better parts of Berlin, but seems to have a strained family live.
In order to cheer up Bernd, the old man takes him along to a meeting of the local group of his party, the SPD (now in government). They meet a former fellow student of Bernd's, who offers him money to write a paper for him for a seminar. Bernd accepts and while collecting material for the paper, he discovers, that the famous Prof. Kolcyk has copied his PhD thesis from an american paper.
Bernd Ziegenhals visits Kolcyk in his office and starts blackmailing him. He is to get 10.000 DM at once and 1500 DM monthly. Kolcyk agrees at this stage but announces, that he is going to fight back. It turns out, that the harmless looking little professor isn't harmless at all.
Bernd tells the old man, that he has inherited money and will move to a little flat in Grunewald, a very nice part of the town. Kolcyk goes to visit the old flat to find out more about Bernd and where he lives now, pretending to be his uncle. Kolcyk rents the other empty flat in Bernd's lodgings to install one of his favorite students, who is also the boyfriend of his daughter.
Mizi's former pimp, who has been in prison, turns unexpectedly up again. He beats up a few of his old cronies (among them Kaleu Thomsen from Das Boot [Thomsen], drunk as usual) and also Mizi, to make her work for him again. Next morning, there are headlines in the newspapers, that Mizi has been murdered and her savings stolen.
Bernd is a suspect, because he has suddenly come into a lot of money. He makes Kolcyk pretend, that he is now his research assistant and gets a regular salary. Kolcyk, who is about to go on a lecture tour to the US, gets a visit from the police. He has been seen with Mizi on the day before her death. Kolcyk invents a story about a research project concerning pimps and prostitutes, which is also the explanation for Ziegenhals' salary. The policeman does not seem to be too impressed by this story but leaves him alone for the time being. Bernd Ziegenhals is also interviewed by the police but can go home again.
On the next day, Bernd gets ill and sees a physician. Tests show, that he has some nervous disease, which makes him very excitable, he is put on tranquilizers and has to see his doctor regularly. He certainly is behaving paranoid, especially, when the professor stops paying. From the US trip, Kolcyk has brought back a statement signed and witnessed by a lawyer, that Kolcyk actually wrote the article for the American author for money.
That seems to be the end but during Mizi's funeral Bernd has an idea. He makes some inquiries and finds out, that the person who supposedly signed that statement, has been dead for a year. The game can continue, now Bernd wants 500 DM more per month.
Kolcyk hears from his student, who lives next door from Bernd, of his health problems. Kolcyk invents some symptoms and visits the same doctor, where Bernd is going. He is prescribed some pills, which, so he is warned, will turn his urine green. Next morning, Bernd's urine is green. After a first panic attack, he calls his doctor and finds out, that the pills, he was sent, were certainly not from the doctor. When a ticking parcel arrives a short time later, Bernd goes berserk and throws it out of the window. It contains an alarm clock.
After these events, Bernd retaliates by starting to court Kolcyk's daughter Jinnie and is quite successful. Kolcyk creeps into Bernd's flat, while he is asleep and switches on the gas of the gas stove. He still only trying to rattle Bernd, he calls from a public telephone and tells Bernd to open his windows and switch off the gas. But Bernd persues his plan and sends flowers to Kolcyk's wife, who is quite in favor of this nice new admirer of her daughter.
Kolcyk then soaks the seats in Bernd's car with petrol, but the only one, who gets burnt is one of Bernd's friends. Bernd arranges a meeting with the professor in a wood and beats him up badly.
Kolcyk's next move is to spread rumour, that Bernd Ziegenhals is telling stories, that the pimp could well be Mizi's murderer and that he even has proof. The pimp immediately goes for Bernd, he kidnaps him in his VW Beetle and threatens to shoot him. Bernd manages to call for help, the police chase them and the chase ends with a bad accident. The pimp is dead and now presumed to be the murderer, but Bernd has survived and is in a better position than ever. He goes on holiday with Jinnie.
Kolcyk, who only went to the doctor to get at Bernd, is told the results of the tests that were done: he has cancer of the bowel. This changes the situation completely: professor Kolcyk makes a last desperate plan, which succeeds. He meets Bernd on an upper floor in a half finished building, where he and Jinnie are going to live. Kolcyk jumps down and makes Bernd look like the murderer.