I  The Doctor had suggested visiting Agatha Christie to his previous companion Martha Jones in Last of the Time Lords, so it was no surprise that the Doctor Who production team decided to follow this up in the next series. And it certainly doesn't disappoint. An Agatha Christie Doctor Who episode is just as good as you would expect it to be, full of murder, mystery and extremely enigmatic characters. In some ways, it is widely different to anything Doctor Who has done before. In others, it feels like perfect Doctor Who. It's a surprise this episode isn't considered a classic by more people as to me this is the quintessential David Tennant story and arguably one of the best celebrity historicals to date.

The Unicorn and the Wasp sees the Doctor (David Tennant) and his companion Donna Noble (Catherine Tate) arrive on the day Agatha Christie (Fenella Woolgar) goes missing. Soon they find themselves with Agatha in the middle of a murder mystery. Professor Peach (Ian Barritt) has been murdered and the Doctor, Donna and Agatha must find out who the culprit is. Was it the owner of the country estate Lady Eddison (Felicity Kendal), the young vicar Reverend Arnold Golighty (Tom Goodman Hill), the war veteran Hugh Curbishley (Christopher Benjamin), the jewel thief Ada Mullins (Felicity Jones), Arnold's brother Roger Curbishley (Adam Rayner), the butler Greeves (David Quilter), Roger's boyfriend Davenport (Daniel King), Indian woman Chandrakala (Leena Dhingra), cook Mrs Hart (Charlotte Eaton) or perhaps even the Doctor, Donna or Agatha Christie?

The Unicorn and the Wasp is a great deal of fun to watch; it is a story that plays to Catherine Tate's strengths as a comedy actor, providing many light-hearted moments. My absolute favourite has to be when the Doctor is poisoned and Donna is tasked with finding a way to shock him out of it. The scene is played perfectly with David Tennant and Catherine Tate, who know exactly how to play the exaggerated facial expressions needed to pull it off. Donna's shock being a kiss is hilarious and helps to enforce that this is a new series Doctor/companion dynamic where they're simply best friends travelling the universe as opposed to yet another romantic relationship.

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loved the 10th Doctor and Rose Tyler together but overall I prefer the 'best friends' relationship between the Doctor and companion as in my view it is much more entertaining to watch and doesn't tire as quickly as the will-they/won't-they of 10 and Rose.

It helps that the pace is so well-plotted by writer Gareth Roberts; there is literally not one dull moment in this story. It rolls along at a rollicking pace and is hugely gripping from start to finish. The murderer never appears too obvious or too stupid; even though it is hard to guess who committed the murders when it is revealed the logic makes a lot of sense.

It is not only a fun comedy episode but also a very strong murder mystery that nicely captures that sort of eery atmosphere of murder mysteries. If there's one complaint I'd have about this episode it's that I wish it was longer - and that's not really a complaint. If it leaves you wanting more, then it has done its job well.

The 'monster of the week' - a giant alien wasp known as the Vespiform - is also one of the new series' strongest CGI designs. The visual created by the Mill is absolutely fantastic and it actually looks like a real giant wasp. If I saw that outside my window in real life, I'd run five hundred miles...and then maybe five hundred more when it starts following me. Wasps are scary enough as it is but giant-sized they are terrifying. The sting from a giant wasp (or 'Vespiform') scarcely bears thinking about.

'Vespiform' is possibly among Doctor Who's most awesome names for an alien race too. It rings off the tongue nicely and feels right as the name for a species of giant wasps. I hope one day Big Finish bring them back for some new series audios as they deserve a return appearance. To me they are like the new series' Wiirn: a race that's obscure to anyone other than hardcore Whovians but are such an amazing concept that they deserve to be appreciated more.

Agatha Christie fans will be happy with Fenella Woolgar's portrayal of the famous author. She is absolutely brilliant in this episode and offers a very endearing portrayal of Agatha; she portrays the author with a fierce intelligence that could almost rival the Doctor's and the way they explain her mysterious disappearance is extremely clever. It's great the way certain new series episodes explore the mysteries surrounding certain historical figures and offer explanations within the Whoniverse for them; I imagine it sparks the imagination of many kids who watch theseries and to me is something Sydney Newman would probably impressed by given that the original brief for the show was for it to be educational.

The reason behind the disappearance may be fictional but many kids won't have even known she had disappeared before seeing this episode. I hadn't known myself as a 12 year old and therefore the show taught me that Agatha Christie disappeared in 1926 and turned up ten years' later with no recollection of what happened.

The way the episode plays with the idea of the bootstrap paradox most recently referred to in Under The Lake/Before The Flood in terms of Agatha Christie's books is also very impressive. The episode suggests that the adventures in this episode subconsciously inspired Agatha Christie to write Death in the Clouds and Donna also refers to the plot of Murder of the Orient Express to Agatha Christie, suggesting that she got the idea of the book from Donna (even if she can't remember doing so). This is another thing I like about the new series that the classic series didn't really do: the way it suggests certain ideas may have been influenced by the Doctor's travels through time and space. Donna may have had to have mentioned Murder of the Orient Express to Agatha Christie for it to have been written in the first place. It's such an inspired idea and one that works well with a show like Doctor Who where the lead character can visit any period of history.

This episode boasts the return of Christopher Benjamin (who previously played Henry Jago) to Doctor Who and whilst it's disappointing that he didn't reprise his previous role it is still great to see him again in this episode. Christopher Benjamin is very convincing as Hugh Curbishly and it is a wonder you don't see him more on television. Age shouldn't be an excuse for not featuring a certain actor if they are still fit enough to act and it is a shame that people of a certain age like Christopher Benjamin are featured so little. He does well despite being 80 years old to continue his acting career; he mainly records Big Finish audio dramas now but recently appeared in David Yates' latest film The Legend of Tarzan as Lord Knutsford.

Overall, The Unicorn and the Wasp is an incredibly fun and entertaining story by Gareth Roberts that deserves more appreciation than it tends to receive. The episode is extremely well-plotted, with a thrilling breakneck pace and the comedy performance from David Tennant and Catherine Tate is hilarious. It's also fun the way the episode plays with the real-life character of Agatha Christie, her mysterious disappearances and in-universe influences for some of her murder mystery books. The Vespiform is a very realistic work of CGI and it is great to see the return of Doctor Who veteran Christopher Benjamin, who still looks incredibly healthy for an 80 year old man. The Unicorn and the Wasp is perhaps the definitive David Tennant episode - it's funny, dark, fast and extremely energetic. Pretty much sums up Tennant's Doctor actually.