Dark Beginnings

I'm finally putting to paper a dark piece set in a modern time with a couple of interesting twists in it. It's a story that has been bouncing around in my head for a few years now and I've managed to put the first and final scenes on paper (well, screen at least).

My problem is that I've just read a compelling article on prose, and one of the key points is something that I've struggled with in the things that I've read and watched: delaying the reveal of something so obvious that your seemingly unaware characters begin to read like idiots; where you want to scream at the pages, "For the love of God, the butler did it!" (As appropriate, of course.)

This has, as I mentioned, nagged me in the content I've absorbed, and since twists and reveals are a large part of my writing, I now find myself on the other end of the issue. How much do I reveal before it becomes obvious and ultimately uninteresting?