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.
(..) you're the secret head of the Temple of the Four Orders in who's headquarters we now sit. Located, north-west corner St. James square I think That's the mystery, the only mystery is to why you bothered to blind fold me at all. Yes... well, standard procedure I suppose. I dare say we have the (..)2009 Sherlock Holmes
(..) inconvene you, sir. But I'm going to have to put this on you. Mr. Holmes, apologies for summoning you like this. I'm sure it's quite a mystery as to where you are and who I am? As to where I am... I was admitedly lost for a moment, between Charing Cross and Holborn, but I was saved by the Bread (..)2009 Sherlock Holmes