"Need to Know" is an episode of the American television series The Twilight Zone. It first aired March 21, 1986.
Often the most perplexing mysteries have the simplest solutions, the most complex questions, the simplest answers. Sometimes we seek them long and hard only to find the solutions and the answers lie right before us in a reference book, under "T" for the Twilight Zone.
Edward Sayers is a government scientist/agent sent to a small town to help investigate a bizarre outbreak of insanity which is spreading through the town. With the help of a local woman, Amanda Strickland, he methodically goes through the town trying to find an answer. Amanda's father just rambles about his dead wife, but gives them a clue in that he had just visited Mrs. Hotchkiss earlier that morning. When they go to see her, she appears normal at first but quickly grows hysterical and threatens them with a knife. Amanda suggests that it may be a disease, since it is spread from person to person.
He eventually discovers that the source of the problem is not a physical disease, but an idea, a single short phrase, that is being passed from person to person by word of mouth. That horrible phrase is nothing more or less than the purpose and meaning of existence, which was somehow discovered by a local resident, Jeffrey Potts, during his travels abroad; his brother Andrew was the first victim of the "plague".
While Sayers is ultimately unable to stop the man from going to the local radio station and telling the entire town the secret, he is able to reach Amanda in time to smash her radio. Only then does she have a chance to point out that she has already had two visitors stop by, and that she has something very important to tell him. She whispers in his ear.
Man is a questioning creature, constantly striving for answers. But there is some knowledge for which he's not yet ready. Secrets once learned overwhelm him. Secrets that for now are best left undisturbed in the Twilight Zone.