Everyone at the station speculates wildly when Dirk is mysteriously called away. Meanwhile, Katja observes the anniversary of her father's death.

Lothar finds out why Nicki is so stressed out about her upcoming exam. Meanwhile, Katja and Ben investigate when someone overhears a gunshot.

Katja learns that the gun found on a teenager is the weapon used years ago to kill her father, who was also a cop.

While Katja, Ben, Henning, and Harry all look into the weapon that has surfaced, Lothar meets Nicki's father, who is a very difficult person.

Katja tells her mom that the police have found the murder weapon that killed Katja's father. Meanwhile, the wife of the top suspect is brought in for questioning.

Everyone weighs their options regarding the suspect's wife, who remains in custody, while Nicki's father proves himself to be a very difficult person to get along with.

Frau Starke finds a diary that reveals that her husband had an alibi, proving he couldn't have murdered Katja's father.

Joe tells Katja that her father actually committed suicide. The others back at the station are unable to find out any information about what happened to the weapon that night.

While Katja deals with the terrible news about her father's death, Lothar argues with Joe about how the situation was handled.

As they consider destroying the murder weapon, Lothar, Ben, and Katja go back to the scene of Katja's father's death.

When the autopsy records reveal that Katja's father couldn't have killed himself, the group realizes it is time to go after the murderer. Meanwhile, Nicki learns that her father is deceiving her.

Both perpetrators are caught in their respective crimes in this final segment, allowing Katja and Nicki to move on with their lives.