In almost every thriller, a point is reached when someone,...

In almost every thriller, a point is reached when someone, usually calling from a phone booth, telephones with a vital piece of information, which he cannot divulge by phone. By the time the hero arrives at the place where they had arranged to meet, the caller is dead, or too near death to tell. There is never an explanation for the reluctance of the caller to impart his message in the first place.