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.
(..) - I know who everyone is. Ah, of course. Uh, gentlemen, this is Lucy, the first woman to... I mean...like I mentioned earlier... Ms. Lucy has for reasons, remains a mystery to me, unlocked certain portion of her brain that offered access to...previously unexplored celebral zones. She has abilities. (..)2014 Lucy