The Secret Adversary, featuring Agatha Christie’s fledgling sleuths Tommy and Tuppence, is frivolous, frantic and funny.

Sarah Punshon, who co-adapted the 1920s adventure with Johann Hari, directs at a breath-taking pace.

A talented cast of seven actor-musicians throw themselves through secret panels and trapdoors designed by Tom Rogers. But this spoof thriller lacks suspense and credibility, mainly because it sends itself up so much, with characters suddenly bursting into song or using a tea trolley as a car. And, when one of the cast asks the audience “Are you following the plot?” there are loud cries of “no.”

Tommy and Tuppence, superbly played by newcomer Garmon Rhys and bubbly Emerald O’Hanrahan, return from the war broke and unemployed.

They become involved in a deadly political conspiracy master-minded by the sinister Mr Brown.

Morgan Philpott excels as the plotting Whittington and a host of other characters as well as coming up with magic tricks, while Elizabeth Marsh plays both the seductive Rita and a bearded Russian Bolshevik.

Excellent support is provided by Kieran Buckeridge, Nigel Lister and Sophie Scott, especially in some slick song and dance routines choreographed by Lucy Cullingford and musically arranged by Alex Silverman.