Averted: "This riddle is quite a mysterious enigma."
Enforced: The producer of a mystery story is also a history buff or just really likes the phrase and wants the work's creators to use it.
Alice: It's a riddle wrapped in a mystery inside an enigma. Bob: Ha, a Winston Churchill quote reference. Nice!
Alice: You're in over your head, Bob. This case is too big for you to solve. Bob: Oh really, is this supposed to be like one of those 'riddles wrapped in mysteries inside enigmas'? Alice: In a word, yes.
Alice: Next, Adam West is going to say that The Riddler has left him and Robin "another one of his criminal conundrums... wrapped in a mystery inside an enigma." Bob: Yeah, he would totally say that!
Bob: It's like a riddle? Alice: It's a bit more complicated than that.