Have you ever sat down to watch TV, and by a completely unexpected twist of fate, stumbled across something so utterly brilliant that it leaves you speechless? Entirely possible... but even less likely when you're watching a program you like, and think you know, and intended to watch just because its on every week. Honestly, I don't watch much TV; I know and like Doctor Who, but this episode just totally ambushed me. It really, really shows how excellent TV can be, and just how rubbish most TV is. I was on the edge of my seat by the end. Its pretty much a completely independent standalone episode, no prior knowledge or interest of Dr Who assumed. Its thrilling, relentless, ingenious, terrifying, and, once more because it deserves it, absolutely ingenious. Solid gold TV brilliance, and all the more amazing that I found it in the stale Saturday night line-up. Seek it out!