I’ve always been a huge fan of Agatha Christie. As a child, she was my next step up the reading curve after Enid Blyton. I used to swap Christies with a rather attractive and well-developed girl at my school called Julia, and it was a splendidly sneaky way of engineering a conversation her. The Dowager Mrs Chrisparkle took me to see The Mousetrap when it was only in its 17th year (work that back) and the creepy tension in it scared me to death. However, since then, we’ve only seen a few Christies on stage and on the whole, don’t think they work that well; and certainly the kindest thing you can say about The Mousetrap now is that it’s a creaky old historical artefact (but you just have to see it once, to prove you’re alive).

The Secret Adversary was only Christie’s second novel and introduces us to Tommy and Tuppence, a game pair of young scamps – well they were in 1922 – full of derring-do and no aptitude for a 9-5 job, who become “Young Adventurers”. They dreamed of hiring themselves out to anyone who needs an escapade performed but doesn’t have the sheer lack of a sense of self-preservation to do it themselves. They’re among Christie’s less well-known detectives, but they’re good fun and full of character, cheek and bravery; seemingly innocent and naïve but with nerves of steel. There was a terrific TV series in the 80s – Partners in Crime – where they were played by Francesca Annis and James Warwick; sophisticated, methodical, good taste and keen as mustard. And I still carry the mental image of those two whenever I think of the characters.

And so to this production, from the Watermill Theatre; I probably should have noticed that before I booked, as it would almost certainly mean an adaptation of an Agatha Christie mystery involving actors playing their own instruments. They love a bit of that down there in Newbury. Miss Marple on the harp? Poirot on a tuba? Fortunately those characters don’t play a part in this tale of our heroic couple searching for a mystery woman with secret papers that would compromise the government, which search in turn leads on to another search, of the mystery man who’s masterminding the whole skulduggery. Tommy and Tuppence get into various scrapes all across London but manage to come up with the solution and even get engaged on the last page. It’s a good story, rather far-fetched and full of coincidences but an enjoyable escapist read all the same.

The adaptation by Sarah Punshon and Johann Hari has very cleverly taken the majority of the elements of the original book and stitched them back together in different sequences and in different locations, which works well as an exercise in itself but for me made the play largely unrecognisable from the original book. The play is mainly set in a nightclub. I’ve had a very good flick through the book today and can’t find any reference to it in Christie’s original – that’s not to say it’s not there, but even if it is, it doesn’t form the central location on which to base the story. The mystery woman has undergone a name change, presumably to support a visual gag in one of the early scenes where a fish lands on a dessert (also not in the original). There’s a medley of songs involving the word “Money” (I’m pretty sure Christie never heard the Flying Lizards), and I surprised myself by realising how much of a Christie Purist Snob I had become.

It’s a shame because there were many elements to the production that were very inventive, very funny and very effective. We both laughed a lot at the primitive PowerPoint presentation of the sinking of the Lusitania; there was an amusingly clever representation of what Tommy saw through the keyhole; there was some magic – always like a bit of magic, I do; and there were moments where the cast addressed the audience, much to our surprise. I loved the clever staging of the scene where the villains are meeting at a table, jutting up from the stage at an angle of 135 degrees with Tommy staring down at them from the grille above their heads. All these elements were performed with a nice sense of fun and an appreciation of the ridiculous.

But we both felt that the whole show was so overwhelmingly tongue-in-cheek, so completely camped up and over the top, that it lost any serious pretence to actually tell the story, or to present characters that weren’t caricatures (I thought only the character of Tuppence herself came close to having any real identity). When the audience returns for the second act, one of the characters asks us if we’re enjoying ourselves and are we following the plot (with a facial expression that implies it’s a pretty tough plot to follow). If the show is doing its job properly, there should be no difficulty in understanding what’s going on. It’s as though the whole thing has been sacrificed on the altar of The 39 Steps but, regrettably, few things are that funny.

We did enjoy the performances on the whole. I liked Morgan Philpott’s rather supercilious array of waiters, MC’s and villains – and I did enjoy his spots of magic. One of the cast members referred to him as “Philpott” during the show – couldn’t work out if that was an intentional “out of character” moment or an epicfail. Emerald O’Hanrahan played Tuppence with a sense of spirit and cuteness which was rather charming. I’ve seen Garmon Rhys before – he was an excellent Wilfred Owen in Regeneration last year – so I know he’s a terrific actor, but I’m afraid I found his Tommy rather one-dimensional. I enjoyed Elizabeth Marsh’s very stagey Rita (straight out of Sunset Boulevard) but sighed with dismay when she donned a beard to play Kramenin – just not enough respect for the original work, I felt.

I think the show went down pretty well with the majority of the audience, but it just wasn’t for us. It wasn’t the show I was expecting to see, and my flexibility biorhythm must have been at a low ebb. I was expecting a classic whodunit; instead we got a 1920s semi-musical end-of-the-pier-show of a whodunit. Purists beware; others may well enjoy. The tour continues to Eastbourne, Ipswich, Derby, Coventry and Kingston, up to May.

P.S. When the interval came we agreed that we were bored by it all; Mrs Chrisparkle proposed taking our coats with us when we went for our interval drinks so that we didn’t have to go back in to the auditorium if we didn’t want to. That was code for I want to go home. However, I didn’t think it quite warranted half-time abandonment, on the grounds that there were some amusing moments and some proficient performances, and I normally only give up on a show after the interval when a play is so bad that it’s not funny. This wasn’t that bad. So we compromised. We went back in, and Mrs C decided to sleep through the majority of the second half. Fair do’s.