(Spoilers for The Unicorn and the Wasp and the whole of Series 4 ahead.)From The Unicorn and the Wasp on, Series 4 hardly strikes a wrong note with me. That is to say, I find a lot to enjoy in each of the episodes. And while I was initially turned off by Gareth Roberts' Shakespeare script the year before, his Agatha Christie story charmed the pants off me (despite the implicit statement on his part that Christie is somehow more brilliant than Shakespeare). And it's not so much the mystery elements that make it work, but the broad comedy I've seen Roberts use on his Who novels, including his 9th Doctor caveman adventure, Only Human, one of the few bright spots in the new series, young adult line.
I've always been opposed to the old Whovian complaint that "it's not Doctor Who" leveled at any story that doesn't meet their IDEA of Doctor Who. Doctor Who has done historical drama, SF, horror, mystery, espionage, satire, and yes, comedy. It's always been a hodgepodge, so there's really no reason this episode couldn't be this stylistically comical (the flashbacks inside flashbacks, for example, or the obvious Clue reference). Comedy in Doctor Who is a tradition that goes back to The Romans, soon on DVD, and that has found its best expression, I feel, in Big Finish' audios. So huzzah for TUATW, a great little episode! It's what Black Orchid should have been, wot!
Since these essays are partly annotative, I thought of tracking down all the Agatha Christie references, but I haven't read a book of hers since my teens! And given that Roberts and Russell T Davies were apparently competing to see how many references they COULD fit in, there should be a lot! So I won't try, and trust you to wiki the damn things.
Things to watch out for
Donna's Destiny: Nothing about Donna's destiny per se, but Agatha's own destiny mirrors hers. Like Donna, she thinks she won't amount to anything (that her books are ephemera), but she is remembered a billion years hence. And like Donna, she suffers from amnesia over the course of this story. Though the episode is largely an unconnected one-off, it has a LOT of thematic links that help keep the various threads in mind like this.
Wibbly-wobbly, timey-wimey: Like here. Though Agatha's amnesia takes care of the paradox Donna might have caused by suggesting Murder on the Orient Express, Miss Marple, etc., but thematically, it mirrors the paradoxes to come.
They call it foreshadowing: The first vespiform making himself human for love prefigures the Rose-Doctor Blue relationship.
Are you my mummy?: Again, Donna and the Doctor are momentarily mistaken for a couple. See the other essays for why this is relevant. And though conceived "naturally", the vespiform is a product of two species, much like Doctor Blue and the Doctor Donna will be of mixed species. And since Lady Eddison had the child in secret, the vespiform does seem to appear out of nowhere, parentless. AND the wasp gets its full identity (and more) beamed right into its brain, not unlike how Donna inherits her Time Lord knowledge.
The bees' knees: Donna again mentions the bees disappearing, and while the episode uses a giant wasp, not a bee, it's meant to create a striking visual that makes the reference to bees easier to notice and remember (especially since it was part of the Series 4 trailers).
The reference section: Donna unknowingly references The Unquiet Dead. The quiver on the Doctor's back may place his adventure with Charlemagne and the mad computer at about the same time as the events of Blink where he was similarly equipped.
The Doctor pulls a few items out of his "C" chest, including a Cyberman chest plate and the trapped Carrionites.
Next week: Shhhh.