STORY LINE (in english):
This episode begins' with a narrator during 'the opening credits in which viewers are prepared for the espionage case.  

In a traffic accident a person named Schobel, who died was identified later as a secret agent from East Germany (DDR) with a false passport.  His wife was informed.  She apparently did not know about the fake identification and she was very angry.  The Hannover police senior commissioner Brammer and the other authorities look over the car and they find a device that doesn't belong to a normal car mechanism.  Further investigation including of its production number identification markings showed that it was a control module for the aiming system of one of four of the military's Leopard tanks.  And that was in the guy's car glove compartment.  
They find out that it was stolen from a military base by sergeant Ulli Meineke after a test shooting.  However, he did not do this voluntarily. 

A few weeks earlier, the Stasi agent Jahn contacted his wife Ina under the guise of a textile representative.  Ina runs a boutique and is in need of money.  Jahn took advantage of this and was able to persuade Ina to photograph her husband Ulli's secret documents.

When Ulli discovered his wife's espionage, he wanted to inform the Military Counter-Intelligence Service (MAD), but refrained from doing so out of consideration for his wife.

When Jahn then put Ulli under more pressure, he agreed to get the entire control module, believing that it would not be discovered.  Now, that the police have found the module and are investigating Ulli's tank unit, the couple panic.  On Jahn's advice, Ulli directs suspicion on his deputy' higher-up 'Lanz by hiding espionage material in his apartment.  Lanz is arrested by the Brammer and Delius of the Military Counter-Intelligence Service when Lanz was in his apartment after he did not show up for duty.  The evidence found in his apartment is overwhelming, but Lanz says he's innocent.

As soon as Ulli thinks he is safe, Jahn asks him to steal the module again.  He again does it and exchanges it for a dummy and leaves the barracks under a false pretext.  After handing over the part Ulli is certain that he will not be able to stay with the troops for much longer and plans to flee to East Germany.  His wife Ina is supposed to come by and he thinks Jahn will help him.  However, Ulli and his wife don't realize how the train systems are restricted by rail when going to East Germany.

Later, during a target practice on the training area , the tank with the wrong module fails and almost hits one of its own tanks.  The barracks are immediately put on alert.  Ulli Meineke cannot reach his wife Ina, and therefore goes back to the apartment.  There he discovers her in the bedroom after she commits suicide out of desperation.  Shortly afterwards, Brammer and Delius arrive and arrest Ulli.'

SOURCE

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 Joachim Wedegärtner and Fred Zander