No clues that I could spot this week, apart from a brief mention of the missing bees thread (and I'm really intrigued by that one; where are they going with that?). The recurring joke about the Doctor and Donna being a couple cropped up again, but I'm not sure that's going to be significant.
I was really looking forward to the Agatha Christie episode, as her mysterious disappearance seemed like good fodder for a Who story, and chucking the Doctor into a murder mystery seemed like it might be fun too, if a little obvious. For some reason, however, it just didn't come off; the mystery was choppy and convoluted in the worst way, with the clues available to the viewer not adding up to the eventual answer. I don't know, but if you're going to present a story as a Christie-style mystery, surely it should work like one, rather than just pay lip service to the genre? They also seriously squandered the author's disappearance, relegating it to an offscreen bit of plot mechanics at the end, when it should have been the core of the story.
I did, despite myself, quite like the nod to Cluedo early on, but they spoiled even that by explaining the joke almost immediately. Bah.