More young Frenchmen – over 1.5 million – died in the Great War than either English or Germans, and the collective trauma of the nation is symbolised in the astonishing story of Anthelme Mangin, a soldier who returned home stricken with amnesia and dementia: he fought for his country and lost who he was.

Sebastian Armesto’s production of The Living Unknown Soldierfor Strawberry Vale and simple8 is based on Jean-Yves Le Naour’s 2002 book, starting with a misguided “parlez-vous franglais” introduction but gathering dramatic force as a host of bereaved widows and parents descend on the asylum in Rodez, central France, to claim Anthelme as their own.

The soldier rises in uniform from a pile of sandbags on a bare stage with a distant vista of the poppy fields. He represents the thousands of “missing” men whom the French authorities assiduously identified over the years as Mangin’s case rumbled on, unresolved, until the start of the Second World War. At the point of revelation, he died.

The actors pass the role among themselves like a baton, so that the character becomes a blank everyman for a nation’s guilt and grief. The stage swarms with a comedy of claimants, Hollywood executives (who have lined up Tyrone Power in the screen version) and a persistent journalist from Le Figaro (handsome Tom Mison), all supervised by the director of the asylum, Feynarou (experienced Tony Guilfoyle), who issued judgements of Solomon twice daily.

An early play of Jean Anouilh, Le voyageur sans bagage, shows an amnesiac Great War veteran in moral conflict with his disgraceful past. Here, we know nothing of Anthelme’s true character, though one rampant widow (beautifully played by Stephanie Brittain), recites a charge sheet of drunken cruelty and abuse. But nothing sticks.

The show is mounted to coincide with the 90th anniversary of the Armistice, not quite sufficient an excuse to answer the question, why this story and why now? Still, as an inventive low-level fringe effort, it is distinctly above average and continuously interesting. The cast includes David Brett, the quirky jackanapes and founder member of the Flying Pickets, and Sue Maund and Hugo Cox conveying the intense desperation of victims and bereaved in the non-stop parade of quick-changing identities.

Economy of dramatic expression fits well with the Arcola’s new policy of “ecologically sustainable” production. The actors’ energy is supplemented by that running off the newly installed hydrogen fuel cell and the new “efficient” lightbulbs everywhere in the building. With a staff of just nine, and a 40 percent increase in Arts Council grant, the Arcola certainly looks like a mean, lean machine revving up for new challenges.

- Michael Coveney