STORY LINE (in english):
On 5 Park Street, a woman shoots a man.  Another is already dead.  Professor Stürznickel a resident there, is one of the two lying dead.  'A burglar, named Neugebauer was shot as an alleged attacker 'of Stürznickel's daughter-in-law Evelyn.  

After some investigation, 'Evelyn is suspected by Essen police commissioner Heinz Haferkamp of having murdered her father-in-law before the break-in and charged. 

Her lawyer Dr. Alexander defends' Evelyn 'during the trial.  It comes out that she may have even known Neugebauger and had a relationship with him.  Alexander is able to 'obtain an acquittal for Evelyn. Probably, due a lot to her step-daughter's stage acting.

Following the trial and 'the death of Stürznickel, Evelyn and her stepdaughter Angela inherit a lot of money and property to which Angela, Evelyn's stepdaughter rejects 'because she was a secret witness to the murder' by 'the stepmother of professor Stürznickel, Angela's grandfather. 

Dr. Alexander, an old friend of Stürznickel, her grandfather is amazed at Angela's new behavior, especially since he only defended Evelyn in the firm belief that she was truly innocent.  

Suddenly,  Angela disappears.  She is found dead in a lake in the Sauerland region, along which the Stürznickels have a summer house next to a waterfall.  Some evidence brings Haferkamp' to suspect 'that Evelyn' was complicit with her friend Dr. Kürschner' in both killing her stepdaughter.  Evelyn is taken away in a police van.  

 During questioning Evelyn admits that years ago she thought her step-father killed her own mother, also possibly at a lake.  They even go to visit the lake in the police van.  Her lawyer Dr. Alexander speaks with Haferkamp and at the end of the conversation out on the lake, her lawyer roughly says: "let's go on to something right", almost as if to say that defending Evelyn in this case is now the wrong thing for him to do.  

Later standing at a table in a restaurant with his ex-wife Ingrid, Heinz Haferkamp talks about the case.  She asks, "if you are found guilty the first time, how can you be found innocent the second time?".  "The proof", he answers.  "Maybe Angela knew that her mother was in on the first murder (of her step-father)" he goes on to say and then right there in the restaurant, he shows his wife what the police investigation turned up: Angela's school Latin notebook where a page is missing.  How did the page go missing and because of who?  "You state the questions endlessly", she says.
Regarding Dr. Kürschner, at line up a witness examines a line up of people who look like Kürschner, but can't recognize him as a person at the scene of the crime.  Later after more questioning, Kürschner is tired.  As questions continue that night at the police office, Kürschner puts his forehead on his wrist on the desk and says "kiss my ass".  "She is sick".  Kürschner says of Evelyn: "that is her motive", he goes on to say with almost sudden new found confidence as Haferkamp, who almost looks bored - like he's wasting his time - fixes his coffee.

'At the next trial, Dr. Alexander's defense is noticeably weak and both her and Dr. Kürschner are found guilty.' 

However, the missing school lesson sheet of' Angela’s 'notebook gives Haferkamp a new idea and he even has Evelyn's lawyer Dr. Alexander’s office searched.  There, the police search locates a farewell' suicide note 'written on what turns out to be that very missing page of the deceased Angela's Latin notebook from school.  Angela had actually written the suicide note and committed suicide at the lake.  Dr. Alexander then' used that note as evidence to make it look like Evelyn and Dr. Kürschner murdered Angela.  Dr Alexander did this in order to get revenge on Evelyn for the murder of his friend professor Stürznickel and for having duped him at the first murder trial.

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')
-- Book written by Karl Heiz Willschrei (Die Abrechnung)