Complex sentence: At the end of each episode, the narrator asked the radio audience how Johnny found the perpetrators, making the show a mystery quiz as well as a drama; those who guessed correctly were entered into a raffle for a prize.
Split into simpler sentences: At the end of each episode, the narrator asked the radio audience how Johnny found the perpetrators. Thus, the show was also a mystery quiz and those who guessed correctly were entered into a raffle for a prize.