With the announcement that the final Hercule Poirot stories will be filmed for ITV this year, confessed detective fiction bore and tedious cataloguer of ways in which the book was better than the film Laura Morgan wonders what we should expect.

I have never been asked to appear on Desert Island Discs, but I have spent happy hours planning what to take with me, just in case Radio 4 should come knocking. My music choices change depending on my mood, but my book doesn’t: ever since I was nineteen, I have turned to Agatha Christie whenever I was ill, bored or miserable, and since banishment to a desert island is likely to involve all three, the Queen of Crime will be coming with me.

(I’m assuming that I will be allowed the complete works. If not, I’ll swap them for Shakespeare, the way you can swap the Bible for your preferred alternative.)

Christie’s stories have been adapted for screens both big and small almost since she started writing them, and while there have been a number of admirable Misses Marple, David Suchet’s 23-year tenure as ITV’s Poirot-in-residence has rendered everyone else’s efforts superfluous. Anorakish types like to tell a story of unclear origin about how Agatha Christie once saw a young Joan Hickson perform on stage and told her “I hope one day you will play my dear Miss Marple”. True or not, it’s pleasing to imagine that Christie could foresee how good Hickson would one day be as the gentle little old lady “with the mind of a sink”, but if Hickson’s Marple is a good likeness, Suchet’s Poirot is perfect: the character sprung from the pages of the books and brought to life. The fussy little walk, the enquiringly cocked head, even the accent, which ought to waver but never does: everything is spot-on.

So we should all be delighted by the news that ITV will be filming the remaining Poirot stories this year: five new episodes, from original stories of, to put it diplomatically, varying quality, which makes it all the more interesting to see what will be done with them.

The best as-yet-unfilmed novel , and the one which I am most excited about, is Curtain: Poirot’s Last Case, which only hasn’t been made yet because you can’t film someone’s last case until you’ve definitely finished filming the rest of them. Set – with a pleasingly Poirotish symmetry – in the same country house as The Mysterious Affair At Styles (the 1916 novel in which the character of Hercule Poirot was first introduced), Curtain was written in the early 1940s and, romantically, locked away in a bank vault until its publication in 1975, and it represents Christie writing at the peak of her powers. It’s a busy, twisty story which should be a lot of fun to watch, not least because it means the return of Hugh Fraser as Captain Hastings, the role for which he is rightly best known.

(An aside: in the books, Hastings has a moustache, and Poirot’s moustache is an extravagant and luxuriant affair, rather than the neat little caterpillar that Suchet sports. The moustaches are the only particular in which ITV’s versions of the two characters have strayed from the way they appear in the books, for which I forgive them on the grounds that big moustaches are hard to act in. Probably.)

At her best Agatha Christie is very funny, and this is often evident in the pairing of Poirot and his hapless sidekick. The early ITV series, in which both characters invariably appeared, were – violent deaths notwithstanding – feelgood TV. They were light-hearted and witty and they spoke of an age of elegance, and painted an affectionate and studiedly beautiful portrait of an England that we would have liked to know, even if it never really quite existed. The attention to detail, both in the scripts and the production, was impeccable; the 1930s costumes and interiors almost – almost – as pleasing as the plots. The original art deco credits sequence was gorgeous, as well as being charming and a bit creepy, making it the perfect opening to a programme that was all of those things itself:

From the early 2000s onwards the tone of the show changed as it began to tackle some of the less lighthearted stories, and to take new liberties with the source material. Sometimes this worked well: the Mark Gatiss-adapted Hallowe’en Party of 2010 was as much fun as the book on which it was based, and added a supernatural touch which fitted in seamlessly and turned the whole into a lipsmackingly spooky affair. Sometimes it didn’t: Murder on the Orient Express, the fanfared Christmas special of the same year, made an unrecognisable character of Poirot, and played around with the ending so much that it wasn’t, in the end, the same story at all. When your source material is one of the most celebrated detective stories of all time, it takes a special kind of arrogance to change the ending. The most charitable interpretation is that ITV didn’t feel they could improve upon the star-studded 1974 version, which – despite Albert Finney’s entirely bizarre turn as our hero – is about as good a straight adaptation as you could hope for, and I think that as soon as you get to the end of this article you should bin whatever you were going to do next and go and watch it.

Some stories don’t need to be mucked about with. Some do, and none more so than Elephants Can Remember, which was written when Christie was eighty-two, and good heavens, does it show. At its heart is a neatish little plot, which is almost completely obscured by the ramblings of a writer too famous to be edited. But whilst it fails as a piece of detective fiction, it is fascinating as an insight into the mind of an octogenarian who is not as sharp as she once was, featuring as it does a procession of characters who can’t remember anything and who repeat everything, often several times in a single speech. The dialogue is baffling, the plot more so, and every so often you have to go back several pages in order to find out who is talking, because everyone speaks like an eighty-two year old. I can’t begin to imagine how they’re going to adapt it for the screen, but I am very much looking forward to finding out.

The third new adaptation, The Labours of Hercules, is taken from a smartly-written, if horribly contrived, set of short stories, the premise of which is so painfully awkward that I’m going to let you work it out for yourself. The stories aren’t individually bad at all – The Stymphalean Birds and The Cretan Bull stand out – and if they can find a way to gloss over the oddness of the initial conceit, it might work quite nicely on TV.

The Big Four is a thriller, not a murder mystery, and Poirot seems appropriately out of place throughout. The plot is disjointed, which makes more sense once you discover that it was pulled together from twelve short stories originally published in The Sketch. My Pocket Essential Agatha Christie (what do you mean, you don’t have a copy?) says of it, snidely but correctly, “Increased sales of the book were arguably due to the author’s disappearance a few months earlier”. There’s nothing wrong with it, exactly, except that Christie’s thrillers are never as good as her detective stories, because the lurch from writing about a world she knows and into one she doesn’t forces her to drop the neat little flourishes which make her portraits of vicarage murders and scandals at the village fete so enjoyable.

On the other hand, thrillers are cinematic, so this might be one of the stories that work better on screen than on paper. Let’s hope so. And if ITV find they can’t cope with the change of genre, they will be back on familiar ground with Dead Man’s Folly, which is such standard fare that you could play Agatha Christie bingo with it. Country house? Check! Afternoon tea in the drawing room? Check! Mysterious foreigner? Check! Angry Young Man? Check! Unhappily married couple? Check! Murdered spoiler Girl Guide? Check!

In the end, the only one which matters is Curtain, because if they can deliver an adaptation worthy of the book it will be a triumphant rounding off of a project that has quietly turned into something rather grand and brilliant, which will make it a fitting tribute to Christie herself, 35 years after her death, as well as a deserved swan song, in this role, for the lovely and clever and luminous David Suchet. Don’t let us down now, ITV.

Laura Morgan blogs at gladallover.net and tweets as @elsie_em.