There's no 'mystery' (to/as to/about) why we're here. = It's no 'mystery' why we're here. [=we know why we are here]
His success is something of a 'mystery'. = His success is a bit of a 'mystery'.
We'll reveal the identity of today's 'mystery' guest after these commercials.
(..) Swine parrot. What is it you do, Monsieur Gadbois? Well, you know, I do a little bit of this and a little bit of that. A man of mystery. One might say that, yes. I would of course tell you more, but it would be safer for you if I did not. Are you all right? Of course I'm all right. (..)1975 The Return of the Pink Panther