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.
(..) Did you quit? Not exactly. Some parents got a kid from Sean Casey's year I think to say somethings about me. Although why anybody would have anything other than peaches and cream to say about me is a mystery. That's a good laugh right? -I'm sorry. -No I get it. I know I've made enemies. (..)2014 Whiplash