As soon as I began listening to this episode I knew I'd "seen" it somewhere before, and was even remembering the scenes evinced by the radio drama.  A little Google and a little IMDB soon revealed the source, which is: The Alfred Hitchcock Hour: Season 1, Episode 6, Final Vow (25 Oct. 1962). Everything old is new again.  What a delectable twist. Thank you, Mr. Slesar.