The Encyclopedia of Old-Time Radio says: "The Adventures of Sam Spade remains today the pinnacle of radio private eye broadcasts."
In 1930, author Dashiell Hammett wrote what is perhaps the most famous private detective novel of all time: The Maltese Falcon. The book was made into a move twice before the ultimate film version starring Humphrey Bogart was released in 1941. Bogie made Sam Spade an unforgettable character, the original hard-boiled private eye.
In 1946, ABC radio brought Sam Spade to the airwaves, starring tough-talking Howard Duff as the title character. The show remained on the air until Duff decided to take a spin on the movies in 1950.
Here's The Farmer’s Daughter Caper, originally broadcast on September 3, 1950.