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.
(..) do for you, Robert? We wanna talk about the Priory of Sion. The keepers? The secret war? Sorry for all the mystery. Leigh, I'm into something here that I cannot understand. You? -Really? -Not without your help. (..)2006 The Da Vinci Code