A female teacher taking part in a school outing to Rome comes to the police station to report that one of her students, Sara Borelli, has been bullied and drugged while she was in the hotel. Interrogated by Terzani, Sara recounts how she had been unwittingly drugged by classmate Clara Moretti. But then Clara's dead body is found just near the police station, having fallen from the bathroom window of her hotel room. What at first had seemed a tragic accident soon turns out to be a case of murder among classmates - and possibly a teacher. But the terrible truth require all Rex's skills and intelligence before it is finally revealed.