Ah, I knew I'd be able to come up with a song lyric title eventually.
So, The Wasp and the Unicorn. I'd place this one below Planet of the Ood but slightly above The Doctor's Daughter, somewhere around a 7. (In view of which I'm going to fix Daughter at a 7, but I'm also going to re-evaluate The Fires of Pompeii from an 8 to a 7, because I think it's more or less on a par with both these episodes.)
I went through a phase of reading Agatha Christie novels in my teens. (It was around the same time as my phase of reading PG Wodehouse and my phase of reading Jeffrey Archer. Dear god, why Archer, you ask? Because it was what the school bookshop stocked. It was that or David Eddings, and I had to draw the line somewhere.) What I learned from that experience was that Christie wrote in a formulaic way, but that you still couldn't necessarily predict the murderer's identity because some vital but absurd bit of information would be withheld until the last minute.
Some years later my erstwhile housemate, the estimable Dr Pittard, explained to me the real value of Christie's oeuvre ("or egg") - she may have had her shortcomings in some areas, but she had a real talent for engineering new ways for the crime genre to work. The murderer had to be the least likely candidate, not simply in narrative terms, but in terms of their mechanical function within the story. One of the victims did it. Everybody did it. The narrator did it. The policeman did it. The detective did it. Maybe you did it. Where were you on the night of Chapter Two?
So this might be seen as a kind of reversal of Gareth Roberts' previous New Who, The Shakespeare Code. The greatest asset of aspiring actor and jobbing hack writer Shakespeare was his understanding of human nature, yet the witches in The Shakespeare Code are after him for his technical ability. Only he can write the pseudo-magic incantation that will release the rest of their kind (or rather, as it turns out, only he can act as a flopping puppet through which they can channel the incantation, so really they might just as well write it themselves... oh, anyway, it's bulwarks). Here, on the other hand, the Doctor needs the help of genre technician Agatha Christie to unravel a murder mystery because only she supposedly understands human nature well enough. Hmmmm.
If Christie really were brought in to work on this story, she'd just wait around until the third murder, throw in a red-herring jewel thief (so far, so good), then contrive some way for the least likely possible candidate to have dunnit. By that token, it really would have been more appropriate if the culprit had been "You, Donna Noble!" or "You, Agatha Christie!" It's not all that Christiesque that the vicar should have dunnit; perversely, it's more fitting that the murderer turns out to be a giant alien wasp. Naturally there's an unlikely family connection disclosed at the last minute ("I loved him, even though at night he transformed into a giant wasp" - what?!). It's ridiculous, but not much more so than Hercule Poirot's Christmas.
What is ridiculous is the vicar's bzzzzzing just before he metamorphoses. I know, I know - it's the vibration of the wings that makes the buzzing sound, not the wasp saying "bzzzzz". That's not why it's ridiculous. He's an alien giant wasp, after all, and in any case a wasp that size ought to sound like a Chinook helicopter close up, so it's not as if they weren't already taking liberties. No no, it's just figging ridiculous.
But it's a comedy episode and therefore can be forgiven much. The shoehorned Christie title references are often quite laboured, but the story overall is a pleasant bit of fluff. Still though, halfway through the season and still no episodes I'd particularly want to get on DVD. Sigh. Next week, the Doctor faces a Dirty Two Dozen of bad pop acts. Oh no, wait, it's Eurovision.