The Rotten Apple Don Matteo helps a motorcyclist who has just been beaten up. On his way to the police station to report the beating, he learns that the victim is an undercover police officer who has penetrated a drug ring. This beating clearly indicates that he has been discovered or betrayed. Don Matteo asks that they re-analyze the cocaine used by the police officer to enter into the drug ring. The results prove that the drug had been switched.