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.
(..) are men of conviction. Mine is to save Dolores or die trying. Wyatt's is to claim this earth or raze it to the ground. But yours... Yours has always been a mystery to me. For all the time we've spent together, I still have no idea who the hell you really are. But happily, in your convalescence, (..)2016 TvShow: Westworld Title: Trace Decay Season: 1 Episode 8