 Mac, Enright and numerous San Francisco cops are on a stakeout outside a drug dealer s apartment building, waiting for the dealer s connection to arrive. When the contact doesn t show, Mac orders the arrest of the dealer anyway. The dealer makes a run for it through the cellar of an adjacent building, hoping to emerge through a third building without being spotted. Enright, tipped off by Mac, runs to the third building alone, with Mac chasing him for his own safety. The drug dealer fires on Enright -- and Mac takes the bullet. Mac is rushed to a hospital for emergency surgery. While he s outside the operating room under sedation, the duty nurse is called away and an orderly pushes a patient into a nearby room. Then someone walks out of the operating room and into the room with the patient. Mac hears cries for help, drags himself off the gurney and investigates. He finds the orderly and another person smothering the patient with a pillow. Mac collapses while wrestling the second person, and is dumped on the corridor floor. When Mac awakens two days later, he continues to claim he saw a murder, which is written off as a medication-induced hallucination. But the drug dealer, who s now in custody, tries to cut a deal by claiming he heard voices from a paging service while talking to his connection. Mac reads a message from his inside informant and translates the key phrase as "a ward for patients." What he witnessed was the murder of an undercover cop investigating a hard-drug ring by posing as a derelict. Mac and Sally go back to the hospital, and Sally s careful questioning uncovers a witness (a bum who feigns illness to get cozy treatment in a charity ward) who was acquainted with the murdered cop, but the witness can t identify the second killer. Meanwhile, the burly orderly (uncredited) knocks Mac unconscious again and takes him to a storage room to kill him. This time Enright saves Mac s neck, but the orderly is fatally shot. Mac declares: "He [the second killer] s already made two mistakes, he s bound to make a third and that will be his downfall." When asked what were the mistakes, Mac snarls: "Not trying to kill me the first time and not succeeding the second!" So what is the killer s third mistake?