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.
(..) might have heard some of the more extravagant rumors about what my plans are, so I just thought you'd like to hear it from me. This is the face. It's no great mystery. I'm an oilman, ladies and gentlemen, I have numerous concerns spread across this state. I have many wells flowing (..)2007 There Will Be Blood