Don't change the channel! Each of this week's radio mysteries involve that exciting new medium - television. A man is poisoned on the air as he's about to reveal a murderer's identity in a syndicated adventure of Boston Blackie, and the cops of Dragnet pursue phony TV repairmen in "The Big Screen" (originally aired on NBC on August 9, 1951). A TV quiz show unravels a perfect crime in "Marked Man" from The Whistler (originally aired on CBS on March 16, 1952), and John Lund stars as Johnny Dollar in "The Philip Morey Matter," as the insurance investigator looks into the nervous breakdown of a popular television star (originally aired on CBS on October 13, 1953).