The disappearance of ten-year-old Mirco on the Lower Rhine made the Mönchengladbach murder investigator Ingo Thiel known twelve years ago. The month-long meticulous search for Mirco's murderer was followed nationwide and, with Heino Ferch in the role of the grumpy, taciturn investigator, an award-winning film was made years ago. The fourth film in the Thiel series is now finished: "Where is my sister?" Arte shows the film on Friday (October 7th, 8:15 p.m.). It is available online until the beginning of November.

Again a real case provided the template. The director is Grimme Prize winner Markus Imboden. Ingo Thiel acts as a consultant for the film, who sets the scene for the beauty and sometimes sadness of the landscapes of the Lower Rhine.

Amelie disappears without a trace after a joint birthday party with her twin sister Marie. Her friend Jonas alerted the police the next morning. Commissioner Ingo Thiel calls the special commission "Amelie" together.

Days pass in which the investigators tread water. The information from the population turns out to be false because it applies to the twin sister who is still alive. But then Amelie's friend Jonas, a popular paramedic, gradually comes under suspicion.

He has an advocate in Amelie's mother Dorothee, played by Martina Gedeck. At first she doesn't seem very affected by her daughter's disappearance, so she gets him a lawyer and gets his release.

But the forensic technology gradually delivers results and finds out: Amelie was pregnant. Doubts arise: did she really not get home that night? And what did Amelie mean when she said to her sister: "I'm not as good as you think."

Heino Ferch once described the real Thiel as follows: "He's on fire, he's always on adrenaline when something like this is going on. He's a stubborn dog who doesn't give in, that's the secret of his success."

As a counterpoint to the investigative work, the film plays with the supernatural: Can the twin sister Marie sense how Amelie is doing? Is it coincidence that she collapsed at a certain time on the night of the disappearance? And what about the knowledge of nature of mother and hairdresser Dorothee, who thinks she can see through her customers when they cut their hair?

The first Thiel film was about the murder of ten-year-old Mirco in 2010 on the Lower Rhine, which the real Thiel was able to solve with stoic meticulousness months later. The second case took place in Duisburg and dealt with the mafia murders there in 2007, in which not Thiel, but the Duisburg investigator Heinz Sprenger was in charge. The third case traced the case of a 14-year-old who disappeared after swimming practice. As with this film, places and times are not reproduced one-to-one in the new fourth film in order to protect those involved who are still alive.

The thriller is far removed from a true crime documentary. The film remains exciting because of its twists and turns.

The role of the very present widow Dorothee (Martina Gedeck) is irritatingly ambivalent: sometimes she appears as a femme fatale in a red leather coat with a luxury sports car - then as a staid housewife in a blue cooking apron. That's how it's supposed to be, but is that a good thing?

A fifth film in the Thiel series is being planned. It is based on a successfully solved cold case from Ingo Thiel's desk.