Doctor Whodunnit? This stylish entry washes away the memory of Black Orchid nicely...

Wasps. What are they good for? Well, as the old song goes, absolutely nothing – apart from to irritate the hell out of you on a hot summer's day. And even worse, they'll sting you without a second thought. At least bees may think twice about this, given that they're committing suicide in the process. But the wasp has no such mechanism to make it as benign, and more to the point, they'll make you look a fool in the process. Whether you're freezing like a waxwork dummy or doing some sort of crazy war dance in a vain bid to get rid of the annoying bugger, they'll still sting you like no tomorrow.

So a giant wasp should scare the bejesus out of any living man, woman or child. No wonder the latest Doctor Who story makes a virtue out of this with a story called The Unicorn And The Wasp. Before this story showed, there was speculation as to how a unicorn and a wasp would fit in with a jolly hockey sticks visit to Agatha Christie in the 1920s. Well, as it happens, the Unicorn turns out to be the name given to a petty common criminal who's posing as a posh flapper. But the giant wasp is real enough, or to give its true title, a Vespiform – which incredibly thinks that the whole world carries on like an Agatha Christie novel, and so kills a few random victims at a garden party held by one Lady Eddison.

In theory, The Unicorn And The Wasp shouldn't hold out much promise. For one thing, it's written by Gareth Roberts who had produced the drivel that was The Shakespeare Code . And he's still channelling Peter Kay by repeating the same unfunny joke over and over again until it hurts. In this case, he throws in numerous references to titles of Agatha Christie with all the subtlety of an elephant in a supermarket. Yes, even to the point where The Doctor says: “Murder at the vicar's rage”. Needs a bit of work, he adds – you think? Or maybe a tighter leash on Roberts' and RTD's silly in-joke which gets wearisome very quickly.

The other obstacle is that Doctor Who's visited the 1920s before with disastrous results in 1982's Black Orchid , a random mess of silly clichés, fancy dress parties in rainstorms and squealing damsels with whippets on their heads. Well, one anyway. So revisiting this time and place doesn't look too hopeful. But somehow, despite these two factors, I quite like The Unicorn And The Wasp. OK, so it's yet another celebrity historical, but it's nevertheless a breezy, enjoyable affair that's brought to the screen with considerable aplomb by the ever-versatile Graeme Harper. Blimey, is there any genre that the man can't tackle?

So what makes this one work and Black Orchid fail? Well, for one thing there's more of a tighter focus in Roberts' script. Whereas Black Orchid was just a random jumble of 1920s sayings and motifs, The Unicorn And The Wasp actually has some sort of plot to propel it along. The murder mystery element isn't as terrifying as The Robots Of Death or The Web Of Fear , but it's still well worked out, and the identity of the killer or its motives isn't easy to spot the first time around. Also, the fact that the killer turns out to be a giant wasp with delusions of a Christie-esque utopia is a pleasingly unusual one, and in fact, there's better ideas at work here in Gareth Roberts' script, which contains more imagination and verve than his previous offering.

Another good reason that Unicorn succeeds where Orchid failed is because there's an actual scary monster at work. The Vespiform is very well realised and is convincing enough to send wasp-phobes ducking for cover or at the very least, picking up a rolled-up newspaper in anticipation. Compare that to the shuffling goon, George Cranleigh, a tragic figure in theory but in practice, rather poorly realised thanks to some rather fake make-up and limited backstory. And while I noted that the alien aspect marred The Fires Of Pompeii , in this case it's not so much of a problem because the Vespiform is the only main threat. There's plenty of sub-plots bubbling away under the surface, but there aren't too many threats spoiling the broth. Or the anchovies. Or the Harvey Wallbangers.

"Even the background music's charming, from the stock cuts through to Murray Gold's well-judged score, which thankfully doesn't go too OTT, as per usual"

Mention of which brings me to another point in this story's favour – it's actually genuinely funny in places. There's some notably good dialogue here – the Christie references notwithstanding – such as Donna's spluttering about Noddy (“Noddy's not real is he? Tell me there's no Noddy?”) or The Doctor's comments about the British stiff upper lip (“That's what they do – they carry on”). And there's also some cases of real slapstick, the most infamous of which is The Doctor's frantic Give Us A Clue scene to Donna. It's a bonkers sequence, part high drama (The Doctor's just been poisoned and desperately needs a cure) and part comedy. It's absolutely mad, as David Tennant rushes around like a madman with a fever, gurning, eye rolling and face pulling in order to get the required cure. Catherine Tate's just as funny, using her comedic background to produce the right delivery of some ridiculous suggestions (“What else? It's a song – 'Mammy!!!' - I don't know, Camptown Races!”). The sequence raises a few chortles on paper, but on screen, it's a near work of genius thanks to the combined comedic talents of Tennant and Tate (good double act name, that) and also thanks to the Main Man Harper.

Yes, a very important difference between this one and Black Orchid. This is a different style of story for Graeme Harper, given that his usual raison d'etre is to successfully helm gritty, uncompromising drama with much style. But he handles the light-hearted matter with great skill, using that old-style rippling flashback technique, complete with accompanying harp. Moreover, he makes you believe that you really have travelled back in time to a hot summer's day in the 1920s. OK, so it's good fortune that the weather was good for this story (unlike Black Orchid), but the production's lovely to look at with the small details covered such as the cars, the clothes and the accessories. Even the background music's charming, from the stock cuts through to Murray Gold's well-judged score, which thankfully doesn't go too OTT, as per usual. A stunning production, which ranks alongside the immaculate Poirot and Marple stories on that rival channel.

His casting's well chosen too, although some of the cast do seem a bit overqualified for relatively undemanding parts. Fenella Woolgar takes centre stage with her near-perfect portrayal of Agatha Christie. Watch this one with the sound down, and she'd even convince you that she was the definite article – all in those haughty cheekbones, I guess. The celebrity historical was starting to get a bit repetitive by this time, but at least Agatha's a real person rather than a one-note idiot who mumbles “Ooh, I must write that down!” It's a return to the likes of Dickens and Queen Victoria – well-known faces, but with a surprising streak of pathos and pity lurking in the background. Like these two examples, Agatha is struggling to overcome her own personal demons (Dickens had been careless with family matters while Queen Vic had lost her husband). Fenella Woolgar carries on the good work established by Simon Callow and Pauline Collins by adding a lot of subtle charm to Christie, a woman who's portrayed in this story as someone who's full of self-doubt and insecurity. Her husband's run off with another woman, for one thing, and her personal lack of fortunes have led her to doubt her own considerable abilities. “Agatha, people love your books, they really do,” reassures Donna. “They're gonna be reading them for years to come.” Woolgar does a splendid job, and again, makes the viewer believe that they're watching a real person than a ham-fisted caricature.

"Felicity Kendall's a great actress, but to be honest, she doesn't really get enough to do as Lady Eddison except stand around and look serene in the background"

Another notable performer is Tom Goodman-Hill as the Rev Golightly. Goodman-Hill plays the part with a slightly awkward, mysterious air that's shifty enough for viewers to point fingers. The only thing that spoils the performance is the fact that a number of fans have pointed out that he's channelling Bruce Forsyth when confronting the two scamps who break into his church (“Put thozzzz thingzzzz back where you found them – itzzzz....”). Whenever I see this, I can't help but think that Golightly should wear some sort of dodgy toupee while ushering Anthea in to give a twirl. But never mind – Goodman-Hill does an excellent job as the baddie vicar, and makes for a suitably threatening presence.

Felicity Kendall though – hmmmm, a familiar face on telly, thanks to The Good Life and no thanks whatsoever to Rosemary And Thyme, a crime drama series that has all the tension of a vicar's tea party. Kendall's a great actress, but to be honest, she doesn't really get enough to do as Lady Eddison except stand around and look serene in the background. She does admittedly get a bit more to do in the last act, when the truth about her son comes home to roost, but it's a little bit too late. Still, Kendall puts in a charming little performance, as does the returning Christopher Benjamin – Hugh is really Jago by any other name, but Benjamin plays these sort of upper crust toff parts so well, and his turn in The Unicorn And The Wasp is no exception. In fact, all of the guest cast do well throughout, even the less demanding roles played by Adam Rayner and rising starlet Felicity Jones as the Unicorn herself, Robina Redmond.

And of course, the two leads continue to impress, whether they're indulging in comedic hi-jinks (see the above commentary), larking around at Lady Eddison's party or helping to solve the mystery. It's nice that The Doctor's just allowed to get on with solving the problem rather than getting angsty or nearly bursting into tears at the latest trauma. It's also fun to see Donna try and integrate herself with the toffs, even breaking into a very obvious fake accent initially (naturally leading to another “No, don't do that” reprimand from The Doctor).

"It's another good example of how a Doctor/Companion team don't have to work around contrived soapy lovey dovey sub-plots"

Interestingly, this was the first proper story to be filmed for this season, but you'd never think it. Both Tennant and Tate have already found that comfortable groove, and even if Tate does ham it up in the odd scene (for example, her angry description of the Vespiform after nearly coming to grief at its sting), there's still that natural chemistry that the two do so well together. And what's more, it's another good example of how a Doctor/Companion team don't have to work around contrived soapy lovey dovey sub-plots, requited or not. It's about The Doctor and his friend simply having fun and enjoying the adventure, and it's another good instance of why The Doctor/Donna team is probably the best out of the Tennant era.

There's no real subtext to be had in The Unicorn And The Wasp. There's no real link to the story arc of the return of Rose or the mysterious disappearing bees. There's no deep 'n' meaningful message or moral high ground to take here – despite the odd snippet about how one day people will value Agatha Christie's books. Instead, it's a rip-roaring adventure that makes a virtue of its 1920s setting and trappings – as opposed to dragging the story down like it did in Black Orchid. It's stylishly filmed, well produced – even the Vespiform POV shots work – and furthermore, a good-hearted and humorous romp to boot. Absolutely top hole.

John Bensalhia limbered up for this mammoth task with a full four-series review of Blake's 7, and writes professionally and recreationally all over the web. Check out his portfolio of work here.

Check out John's previous Doctor Who review, The Doctor's Daughter

IF YOU ENJOYED THIS ARTICLE, PLEASE HELP SUPPORT OUR SITE, AT NO COST WITH ONE CLICK ON THE FACEBOOK 'LIKE' BUTTON BELOW:

If you're interested in writing for Shadowlocked (disc and screening reviews, etc, or just getting some extra coverage for your extraordinary writing talent, get in touch with us.