STORY LINE (in english):
'The American millionairess Vivien has found out' that 'her former husband and mob key witness Franz Scheller' is 'in Germany..  He lives there, hidden by the American Federal Bureau of Investigation (FBI), as a photo lab technician.  Franz Scheller even has a new wife in Essen.

Since Vivien wants to win him back, she sends mob lawyer Mr. Whitman to Scheller's photo shop to contact him.  With very dramatic classical music occasionally playing in the back ground alternating with periods of eery silence, Scheller who now sees his disguise lost, follows Whitman on his way through the city and finally on a boat.  He notices his pursuer and takes a picture of him.  Little does Whitman know that Scheller is pursuing him by car in order to kill him, visiting more than one boat terminal chasing a ferry that he is on.  After getting off a ferry, Whitman is ambushed by Scheller and shot with a rifle by him.  On foot, Scheller quickly runs over and a crowd of by-standers has quickly developed around the dead body.  He asks a few questions and leaves.  

Back in Essen, police senior commissioner Heinz Haferkamp is entrusted with the investigation of this murder and through the photo in Whitman's camera, his attention turns to Scheller's.  Haferkamp learns that Scheller had previously set fire to the mailbox in which Whitman had thrown a postcard to the mob boss Titus Capelli, against whom Scheller once testified.  "New York. Dear Titus, you won't believe it": read Haferkamp from the post card aloud in broken-sounding english.  Did Scheller's wife VIvien ask Whitman in on this or did she even know?

Haferkamp visits Scheller.  They talk about his rifle.  Haferkamp says things like: "It was only one shot, Mr. Scheller" or "You said the name Capelli, huh?"  Scheller is having his rifle checked, whereby Scheller is withholding the murder weapon from commissionier Haferkamp. 

Still in Germany, Haferkamp questions Vivien, asking if she knows Titus Capelli.  She says "no" in an unusually quiet voice.  Or if she knows two men in a photo with one of them possibly being Scheller.  She says "no" again the same way.

Haferkamp questions Scheller again.  Scheller seems like he's in a hurry. "Where were you during the murder?"  Haferkamp asks. "In Italy" answers Scheller, immediately. Since his employee Claudia has noticed that the police are investigating her boss, she begins to blackmail Scheller. 

Haferkamp says to his wife in a restaurant that in Germany witness protection is able to occur when someone dies, the protected witness takes their place. 

As a result, he' backs 'more and more into a corner as Scheller is unable to kill Claudia in order to silence her or to talk her extortion demands down to lower levels, especially since she warned him that she had deposited the incriminating information in a closed envelope with a notary. 

Scheller then tries to win the requested amount' during 'an illegal poker game.  With Scheller's hand, he is confident of victory. However, his opponent has four aces.

While Claudia is developing pictures of a horse show in the darkroom,  Scheller discovers a picture in which he recognizes Vivien. 

Suddenly Scheller's new wife finds $80,000 in a box in the house before Scheller talks with her when he gets home.  Strangely enough, it is the same amount that Claudia asks for hush money in Deutsche Marks.  His wife accuses him of having withdrawn the entire joint balance.  But he cannot explain how the money got into his house.

Haferkamp and Scheller meet again in a bar.  Haferkamp is asking questions like: "What are you going to do with all of this money?" and "What will you spend it on?".  Scheller finally says: "I don't know". 

Since, he now knows that Vivien is in Germany, he sends her a message.  The two of them communicate by phone then finally meet at a ranch as Scheller is surprised by a familiar mob hitman.  Vivien appears and shoots the hitman.  Scheller is grateful to her and she then explains to him that Whitman's appearance, the blackmail and the killer, and finally the deposit of the 80,000 dollars were only initiated by her to make him flee back to America with her.  So, Vivien knew Scheller had a new wife.  "I am your wife" she says directly to him.  Scheller pretends to accept it and takes Vivien and the money to a private airport.

Haferkamp continues to investigate with Kreutzer.  They visits the embankment where the hitman's body is found.  He "was thrown from the car ... the doctor said .. maybe four hours ago": Kreutzer says.  Suddenly, Haferkamp says: "Oh, crap!" and starts running back to their car.  Then he visits Scheller's second wife in Essen.  She tells Haferkamp that Scheller took all the money she had found in the house.  It seems like he hasn't been back, yet. She goes on to say: "But, this American, this Whitman, he was killed, no? ... He did it. I know it. He told me."

Haferkamp leaves the second Mrs. Scheller after finding out about her husband's past life and she saying that she did not know anything about it and she also reports to the inspector that her husband had behaved strangely for some time and has now disappeared.  

It is clear to the commissioner that Franz Scheller wants to rebuild a new identity.  Next, the commissioner is able to find Scheller at a small airport during a large manhunt by the police. 

In the meantime, Scheller is readying a business jet for take-off.  The hostess of the plane introduces herself.  He and Vivien get on board and toast with drinks.  Then, he tells her he forgot his camera.  He says stops the plane.  He gets off.  When he gets back on the plane, Vivien is only semi-conscious and seems sleepy.  Scheller tells her to sleep.

Meanwhile, the police have tracked Scheller down to where he now is and Haferkamp is on a helicopter flight there.  

With Vivien still unconscious in the passenger cabin, Scheller asks the pilots to stop and let him out again, yet continue on with his wife on board for the flight.  Now, Scheller stands on the taxi way as the plane is leaving.  Then, Haferkamp's helicopter lands right there and he gets out and chases Scheller through a hangar.  Haferkamp takes him into custody in a front office, there.  Scheller says he installed a bomb on the plane and he planed to disembark before departure and fake his death over the Mediterranean.  

Haferkamp is able to prevent it at the last moment and Vivien is also taken in for murder.'

SOURCE: (updated)-- 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')-- Book by Karl Heinz Willshrei