It's kind of tricky at some points to figure out who's who, but it's not really two couples; it's a bridal party.  Bride, groom, best man, maid of honor.  David and Eve are about to be married.  Hank and Barbara aren't dating.

It isn't so much a supernatural story as an action/adventure story, and not a bad one for radio where you can't actually see the whirlpools and the death-defying gymnastics.  The ending is very satisfying.  Action/adventure, questioned supernatural elements.