The Secret Adversary is another of the Watermill’s actor-musician productions, and it starts with a rousing version of Look for the Silver Lining. But this isn’t a full-blown musical; the music is more of an accompaniment to the main action.

The play is an adaptation of Agatha Christie’s first Tommy and Tuppence thriller, where our heroes are in a 1920s Britain recovering from the war and facing political unrest, unemployment, strikes and Communist threats. After leaving the army, the unemployed Tommy meets his old friend Tuppence. Both are short of money and looking for some excitement, which quickly comes their way. They are persuaded to help the government to find a mysterious Jane Fish, who has a document the government needs (there is a delightful silhouette depiction of the sinking of the Lusitania, from which Miss Fish is a survivor).

Tommy and Tuppence are played by Garmon Rhys and Emerald O’Hanrahan with just the right level of naïveté, energy and enthusiasm. The other five in the cast play a variety of major and minor roles, as well as the instruments.

Morgan Philpott, as the baddie Whittington, is menacingly evil and is excellent in his smaller roles. His singing of You’ll See Him in Your Dreams is deeply sinister and disturbing! Elizabeth Marsh is on great form as Rita the dancing diva and Kramenin, the Bolshevik agitator with the unlikely beard (not forgetting the manic French chef), and the quick changes between the two costumes must cause some backstage headaches.

Nigel Lister, as Sir Julius (PC, KC, MP, MBE, …) is suitably authoritative and Kieran Buckeridge plays the American millionaire. Sophie Scott plays Annette, and also gets the chance to do some dancing.

This adaptation is a potpourri of styles, with elements of musical, farce, slapstick, magic and melodrama. Perhaps surprisingly, this seems to work, producing an adult version of a children’s show. The language, although rooted in the 20s, has had skilful modifications from the adaptors and is not in the least stilted.

Designer Tom Rogers’ set has a front apron, with an enticingly sinister, somewhat gothic, many-doored cavern behind it which provides an excellent setting for the many different scenes, and allows for quick and effective scene changes.

The production, directed by Sarah Punshon who is also the co-adaptor, is great fun and the acting is good although the pace throughout needed to be speeded up.

PAUL SHAVE

Christie... the musical

What would Agatha have to say about it?

The Secret Adversary, at The Watermill, Bagnor, until March 21

As a fan of Agatha Christie, I wasn't sure what to expect from this adaptation by Sarah Punshon and Johann Hari. I found they have achieved the impossible task of mixing the storyline with a joyous medley of music, magic and mirth, never too much of any of the latter three, always entertaining.

A brilliant and completely unexpected start has the cast singing Look For the Silver Lining, giving a clue to what is to come.

Set in the 1920s, young Tommy and Tuppence, home from the Great War, decide to become Young Adventurers and an unpaid bill leads to them being given the task of tracking down one Jane Fish.

Jane, who has now disappeared, was a passenger on the ill-fated Lusitania and was given the draft of a secret treaty.

A shadowy figure by the name of Mr Brown is desperate to retrieve the papers, which could cause revolution in Britain, and the young couple have only a few days to find Jane and avoid disaster.

So much for the original story. Added in are the superb cast, and the extraordinary elasticity of a fantastic stage set which enables fhe cast to dash in and out (and up and down) the stage at a pace which leaves the audience breathless.

Garmon Rhys (Tommy), in Fair Isle jumper and Brylcreem, and Emerald O'Hanrahan (Tuppence), with her bouncing bobbed hair and so-bright smile, capture the feel of the era and bring to life the Christie characters exactly.

Hard to believe that Rhys has just left drama school, this was such a mature performance.

It is impossible to speak too highly of the actor musicians who back the young couple - Sophie Scott (Annette), Elizabeth Marsh (Rita and the bearded Kramenin), Nigel Lister (Sir James) and Kieran Buckeridge (Julius), while Alex Silverman's mix of snatches of modern and Twenties' music enhances the action.

Magic is in the safe hands of Morgan Philpott as Whittington.

Not only could the very funny Philpott do sleight of hand, but he has the knack of being a man of a thousand expressions without moving a muscle.

Chosen for the world stage premiere of the 1922 crime story The Watermill can be proud of this outstanding production, directed by Sarah Punshon.

And that sound isn't Agatha Christie turning in her grave - she's cheering.

CAROLINE FRANKLIN

The former Independent columnist Johann Hari has been keeping a low profile since leaving the paper in 2011, in the wake of a furore that associated his name with charges of plagiarism, misattribution, fabrication and even nasty online back-biting under a pseudonym. But now the arch lefty has resurfaced in a surprising fashion - as co-adaptor of one of Agatha Christie’s earliest novels, in the genteel locale of Newbury’s lush Watermill Theatre.

I enjoyed what he and Sarah Punshon (who also directs) have done with the first adventure featuring young have-a-go sleuths Tommy and Tuppence. The Secret Adversary (1922) has been whittled from 320 pages into a fun two-hour show, with justifiable liberties taken.

I’d give more than tuppence, however, to see Hari turn his fall from grace into a one-man confessional or fictional drama. In a sense, and maybe this is the self-effacing purpose of the exercise, any hack could probably set to work licking this lesser-known thriller into theatrical shape.

True, there’s a strong political element to the complex yarn – which involves plotting trades-unionists, Bolsheviks and Irish Republicans, and taps the uncertainties as well as the forced gaiety of the Twenties. And perhaps Hari’s internet subterfuges led him to favour a storyline featuring an elusive puppet-master called “Mr Brown”.

Even the opening pastiche-Twenties song, urging us to “look for the silver-lining... remember somewhere the sun is shining”, could be read as Hari hinting that he has weathered the storm.

In general, though, this old-fashioned affair has a run-of-the-mill, in-house feel to it. A multi-tasking, seven-strong cast of actor-musicians work their socks off, on a dinky set beautifully designed by Tom Rodgers – which uses picture-book, warped perspectives to help conjure a tongue-in-cheek air of suspense and wings us right across town from The Ritz to cabaret joints and shadowy meeting-places.

The evening – inclined to stoke confusion with so many deferred revelations – is held together by the glue of Alex Silverman’s retro music, recurrent bouts of accomplished magic from Morgan Philpott, and a convivial air of frantic invention that recalls that long-running stage-hit The 39 Steps.

If it’s only one knowing step above amateur-dramatics, there’s no doubting the polish of the players or the quality and promise of the leads, Garmon Rhys’s Tommy and Emerald O’Hanrahan’s Tuppence. The pair look so peachy-perfect in their dapper costumes, and are so infectiously animated by their escapades, they seem to embody a thoroughly welcome sense of budding, near-at-hand spring.

DOMINIC CAVENDISH

Commemorating the 125^th anniversary of Agatha Christie’s birth, The Watermill Theatre, in association with Eleanor Lloyd Productions, has created a cracking world stage première of The Secret Adversary.

This splendid Tommy and Tuppence thriller cleverly adapted by Sarah Punshon and Johann Hari is an inventive funny spoof played at a breathtaking pace by the seven highly talented actor-musicians.

Tom Roger’s luscious design is highly ingenious with secret panels and hidden trapdoors and a stunning arch with lights. The period costumes are spot on.

Set in 1920, our intrepid heroes, Tommy, impressively interpreted by Garmon Rhys who recently graduated from drama school, and the plucky Tuppence, beautifully played by chirpy Emerald O’Hanrahan, return from the war flat broke and unemployed.

They embark on an outlandish business scheme establishing “The Young Adventurers Ltd—willing to do anything, go anywhere.”

Their first adventure involves international intrigue, covert treaties, undercover agents, disguises and blackmail—quite a heady mix. Moreover, they need to discover the disappearance of diplomatic papers and find out who and where is the mysterious Jane Finn who disappeared when the Lusitania sank? And who exactly is Mr Brown?

Elizabeth Marsh is the seductive resolute Rita and many other characters, including the Russian Bolshevik, Kramenin, complete with beard, and is totally convincing.

Gun-carrying American millionaire Julius P Hersheimer (Kieran Buckeridge) is also searching for Jane Finn and so the race is on to find her.

Philip Morgan plays the conspirator Whittington as well as myriad other characters all to great effect as well as performing some clever magic tricks. He develops a wonderful rapport with the audience. The car sequence is hilarious.

Completing the cast is Nigel Lister as the prominent attorney and Sophie Scott as Annette.

The plot, as you would expect from Agatha Christie, twists and turns but we are kept guessing until the very end.

There is so much to delight in this rollicking fun play including music pastiches, a comical, thrilling chase scene and some striking song and dance routines choreographed by Lucy Cullingford with fine musical arrangements by Alex Silverman.

ROBIN STRAPP

If you’ve seen the widely toured West End hit The 39 Steps — a gleefully frenetic, slickly comic take on the John Buchan thriller — then this wisp of frivolous froth, based on an early Agatha Christie novel, may seem less than fresh. Yet as co-adapted by the former campaigning journalist Johann Hari and Sarah Punshon, who also directs, it serves up a palatable confection of jolly japes, musical interludes and nifty stage business, modestly garnished with politics.

It could move more swiftly and the convoluted plot isn’t compelling enough, but the actor-musicians are winning and Tom Rogers’s designs are an elegant triumph of ingenuity and wit.

Christie’s 1922 story introduced readers to the plucky young adventurers, Tommy and Tuppence. Here, in a climate of post-war austerity, the duo are jobless and cheesed off by money worries and a diet of stale buns — although Garmon Rhys’s affable Tommy and Emerald O’Hanrahan’s game, glossy-bobbed Tuppence look frightfully good on it.

They collide at a London nightspot when Tuppence is caught attempting to abscond without paying for her dinner. Panicked, she blurts out a false name, inadvertently plunging them both into international intrigue and the revolutionary machinations of a mysterious, power-hungry criminal mastermind known only as Mr Brown.

Sinister, bearded Russians, Bolshie trade unionists and menacing Irish Republicans are the tools of this shadowy villain, but the show’s tone is never permitted to darken and none of it matters much. Rogers’s set, with its pop-up trompe-l’oeil effects and surprise trapdoors, whisks us between seedy backstreets, taxi rides and the Ritz and Alex Silverman’s music cheekily slips reworked pop songs — Madonna’s Material Girl, Jessie J’s Price Tag — into its Roaring Twenties pastiche. It’s all dizzy and diverting, but it scarcely offers so much as a cocktail olive to chew on.

SAM MARLOWE