The "Don Giovanni" premiere at the Stuttgart Opera was a roaring success, so the premiere party is correspondingly lively. Intendant Bartholdy especially praises the bassist Cassian Pfeiffer, who sang the Steinernen Gast and thus celebrated his 20th stage anniversary. The buffet had just opened when Dr. Arnulf Sontheim, who is closely associated with the house as a voice specialist and chairman of the circle of friends, is found stabbed to death behind a pillar. It quickly becomes clear to Bienzle and Gächter that the perpetrator is to be found in the vicinity of the opera, because the murder weapon is a prepared hunting knife from the armory. Allegedly, Sontheim only had friends and admirers in the theater: soprano Sylvia Temesvari, for example
was a loyal patient, Cassian Pfeiffer, a regular visitor to Sontheim's practice, even describes the doctor as a close friend, director Bartholdy took advice from him. Anita Breitling, his receptionist, can only praise her former boss in the highest tones. His singer patients received strength and security from him. But Bienzle also hears undertones of reserve, for example with Sylvia Temesvari, who has recently stopped visiting the practice frequently. The more Bienzle finds out about Sontheim, the clearer the picture of a man who has made others dependent on him becomes clearer. Either through his medical work, in his relationships with women, or quite tangibly, as in the case of the director, to whom Sontheim lent a large sum.
One wonders whether a member of the opera forcibly freed himself from this dependency. Stage manager Robert van Dahlen is deliberately calm and relaxed, although until recently he was the celebrated baritone at home and a constant patient of Sontheim before his career ended with paralysis of the vocal cords. He doesn't hold a grudge against the doctor who couldn't help him, he emphasizes again and again. Cassian Pfeiffer, on the other hand, consistently avoids Bienzle. Only when he visits him in the hospital does the inspector manage to speak to the singer. Cassian spends every free minute there visiting his daughter, who is in a coma after attempting suicide. Like Waltraud Pfeiffer, his wife and dress mistress at the theater, he is longingly waiting for Sarah to wake up again. The mourning for Sontheim has already faded into the background again.
The longer the investigation lasts, the more unrest and rejection spreads in the opera house: the operation must go on unhindered, which is just as important to the director as it is to his singers. The commissars get in the way. But Bienzle believes he knows that the perpetrator is to be found in the vicinity of Sontheim's patients. And that Robert van Dahlen is hiding a lot from him. But just as Bienzle wants to get the stage manager to tell him the truth, van Dahlen is attacked on stage..