STORY LINE (in english):
'Isabel Raisch works as a waitress in a country inn.  Although she is married, she is not averse to' leaving with 'other men.  Her current lover is Gerhard Helm from an Essen construction company.  When he picks her up from work for a trip, they have no idea that her husband Peter Raisch has caught on to her running around on him and is following them.  

But, he loses sight of her' suddenly as 'Helm's car runs out of gas.  Helm leaves Isabel alone at a lonely forest crossing to' go and get more 'gasoline from the next town.  When he returned, he found Isabel seriously injured next to the Audi 100.  He hurries to refuel the car and tries to get the woman to the hospital.  However, she dies on the way and Mr. Gerhard Helm decides to hide the body in the forest for fear of a scandal.  A little later the shoe dealer' named Mr. Kurmeier appears at the same intersection and he appears to look carefully for something on the floor and he finds a metal letter "R" and pockets it.

Shortly before the end of the' workers and others' night 'shift at 6 a.m., the city of Essen's police senior commissioner Heinz Haferkamp and his assistant Willy Kreutzer are called' in 'to the same intersection where some children have found the body of a forest worker in the bushes.  Also, a blood-smeared stone and a gasoline stain are found near the site where Helm's car was parked.  A small piece of metal is also discovered.  A short time later, Haferkamp and his police assistant Kreutzer are called to a point in the forest about two kilometers away, where Isabel's body was found by fellow forest workers.  

Since the blood on the stone is eventually found to have been from 'Isabel,  Haferkamp researches her surroundings and has all men with whom she has contact questioned.  He also arrests her husband Peter as the main suspect.  The dead man's notebook contains the official telephone number of Mr. Helm, whom Haferkamp visits in his office.  

The gasoline stain leads the commissioner to check the gas stations in the vicinity of the crime scene.'  Maybe the particular gas in the gasoline stain can be matched with that from a particular gas pump at a place that was at a particular time.   'At the station in question, Haferkamp tricked Helm by falsely claiming that the gas station attendant recognized Mr. Helm.  Gerhard Helm admits to have been there and describes what happened in the police station.

But, now Mr. Helm is under suspicion of murder also because his wife incriminated him by destroying evidence: she removed the suspicious petrol can and may have brought some of the car's stuff to the washing machine.  All in her own way, to try to help him.  So, Helm is taken into 'custody, and the authorities let Helm's wife come to visit him in the prison, "So that the two of them can talk, maybe that will make a difference".  In a key point, Mr. Helm's wife eventually says to him: "You just have to say one word and I'll help you".  

So, this let's the authorities who are no doubt listening know that she knows what happened, etc.. but all she wants is an apology and if she gets it, then she will turn against the law and help him.  But not before, apparently.  But of course, Mr. Gerhard Helm does not understand her hint' and even if he could, he probably couldn't care less.  So, he just gets angry and goes back to the cell.

Haferkamp orders that Mrs. Helm' be shadowed by the police in order 'to find out whether she has set a trap for her husband or not about his affair.  A house search results in a large sum of money and a recording device and' cassette tapes. 'Surprisingly, this relieves the burden on Gerhard Helm, because the device was hidden in his car without his knowledge at the time of the event.  It contains the whole act on the "play" button and it leads to Kurmeier.  An inscription with a damaged letter "R", to which the metal piece fits, is also discovered on his company car.  Kurmeier ran over the forest worker because he' was driving' - ladies and gentlemen - 'completely drunk?  Isabel had observed it.  It was recognized by Kurmeier,' too, who 'then tried in vain to bribe with money and' if that didn't work, then finally strangle and kill his way out of panic or to get killed?

The money found at Mrs. Helm's place had been extorted from Kurmeier.  Since her husband was imprisoned for' an act of manslaughter that he supposedly 'did not commit, she found it compensatory that Kurmeier paid for someone else - Mr. Gerhard Helm - to sit in jail for him. 

And, so the strongly' religiously inclined and opinionated wife Mrs. Helm 'had therefore tried to punish her husband for his infidelity by suppressing' and trying to hide the 'evidence.  Why?  Because', all she wanted was a plea' and a request for 'forgiveness from her husband for the infidelity and 'then she would have helped him.'
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SOURCE: (updated)from Wikipedia Germany, Wikipedia the free encyclopedia
-- https://de.zxc.wiki/wiki/Tatort_(Fernsehreihe)#Liste_der_Tatort-Folgen
(see: 'Main article : List of crime scene episodes')