Someone left an envelope with a riddle inside it for Wayne. His secretary asks him: -- Who would send you a riddle? -- That, Maggie... is the riddle. Batman Forever, movie "Who would send him a riddle is for sure a riddle. But what is the reason for using THE here? Does he mean that what was in the envelope is just an ordinary riddle, but this one (who sent ...) is a special one, and that's why THE is used? Thank you.