The Watermill and designer Tom Rogers work their magic once again with an elegant set that looks positively cavernous, complete with multiple exits and entrances through doors and trapdoors. These allow for the thrilling chases vital to this adaptation of one of the earliest thrillers from the pen of mistress of the genre Agatha Christie, the 125th anniversary of whose birth we celebrate this year.

Brave and resourceful bright young things Tommy and Tuppence make their debut in this tale of derring-do, cross and double cross (they would reappear periodically, ageing gracefully in subsequent adventures, ending as heroic grandparents!). The setting is immediately post World War One, when there was a perceived and perhaps very real threat of anarchy and revolution in the West, thought to implicate Bolsheviks of Russia and domestic Bolshevism - and even the suffragettes.

Our heroine may be called Tuppence, but she is actually penniless, so armed only with cheek and intelligence, she and newly-demobbed Tommy (perhaps his name is a tribute to real-life fighting men), decide to hire themselves out - "no unreasonable offer refused".

In no time at all they are embroiled in a terrifying plot to bring anarchy and violence to the streets of London. Who is the missing American Jane Fish, who escaped the sinking of the Lusitania armed with secret papers vital to international security? The hunt is on as mistaken identities, sinister bearded Russians, merciless poisoning and threatened executions all lead to - and seem to stem from - the mysterious and unscrupulous man whose alias is 'Mr Brown'.

The treatment is as deliciously deft and light, even daft, as regulars have come to expect from the Watermill. Yet the parallels with the present are there. Think of poor poisoned Litvinenko and terrorist action on the streets of Europe's cities.

Let's concentrate on the fun though, starting with deft magic from MC Morgan Philpott, as this is a musical show within a show. There's musical magic too, from every talented member of the seven-strong cast, who juggle instruments and mostly multiple roles with huge aplomb.

I'm glad I didn't read my programme in detail beforehand, so it took me a while to realise with delight that the sinister tall, bearded Russian was actually statuesque Elizabeth Marsh doubling as a veteran cabaret artiste! Sophie Scott is perfect as plucky French Annette, Kieran Buckeridge is a convincingly forceful American millionaire and Morgan Philpott's Whittington and Nigel Lister's Sir James are convincing true-blue Brits - but are any of them really what they seem...?

Emerald O'Hanrahan and Garmon Rhys play Tommy and Tuppence to the hilt and make a sparky double act. Sarah Punshon (who also directs) and Johann Hari have adapted and simplified Christie's labyrinthine tale with some panache and Alex Silverman's original music and arrangements meld seamlessly with period classics to evoke a real sense of period.

A plaudit too for the wonderfully attractive and informative programme. A topping start to the Queen of Crime's anniversary year.

The Secret Adversary continues at the Watermill to 21 March then tours to 9 May