When a woman is brought to a hospital, the doctor who sees her, believes she has diphtheria so he calls Dr. Ross, the hospital's virologist. Ross wants to wait till they can confirm it. Ross tries to reconstruct her life to find out how she came into contact with it. He tries to get help from the police but the captain is more concerned with locating a man who killed a couple cops. When more people who are infected come in, Ross tries to find the source and when he uses what clout he has to get the captain to cooperate, he gives one of his detectives to help him.