Dessert, Southwark Playhouse review - undercooked and overwrought

"What is this, Saving Private Ryan?" a character randomly queries well into the actor Oliver Cotton's new play, Dessert. Well, more like a modern-day An Inspector Calls on steroids, with the volume turned up so high in Trevor Nunn's production that you don't half believe the questioner's wife when she talks about a state of affairs that could be heard all the way to France.

After a promising and prickly start, Cotton's hectoring satire of our recklessly self-absorbed, increasingly divisive age devolves into implausibility and hysteria in equal measure. The result is less enlightenment than exhaustion all round. 

Imagine the unseen Eva Smith from JB Priestley's play risen from the dead to castigate the privileged classes that led to her abject end, and you have an antecedent of sorts for what happens here. As Dessert begins, two eminently comfortable couples are nearing the end of a splendid-looking dinner served at the sumptuous home of squillionaire Hugh (Michael Simkins, snapping forth words like "Cirencester") and his wife Gill (Alexandra Gilbreath, an uncanny soundalike here for Diana Rigg). Their American guests are an investment world bigwig called Wesley (Stuart Milligan) and his unapologetically philistine wife, Meredith (great choice of name) – a tired variant on the dumb if moneyed blonde whom the wonderful Teresa Banham (pictured below) invests with more dignity than the part deserves.

Written as a walking catalogue of incomprehension, she can't let pass mention of such diverse subjects as Broadmoor prison or the language Pashto without making clear that she has no idea what is going on. Interestingly, too, Meredith takes no interest whatsoever in art (isn't this just the sort of person who would be a docent at New York's Met?), so is nonplussed when the collector that is Hugh trumpets his purchase, for a comparative song, of a painting that might just be a Giorgione worth eight million pounds. 

The initial sequence has a commendably take-notice energy as the two couples talk over and around one another, like a collection of Wallace Shawn-scripted swells just waiting to be laid low. It helps that Rachel Stone's set may be the single most elegant design I've yet come across at Southwark Playhouse: surely a bidding war awaits for those gorgeous settee cushions once the run ends. The competing banter at the start is followed by gales of laughter with the emergence of the evening's cook, Roger (Graham Turner, pictured below), a onetime "City crackup" who makes brilliant comic hay of his inability to remember precisely which herbs contributed to the meal's success. Who knew tarragon could be a punchline?

Cotton, the, um, seasoned performer turned playwright whose Daytona ran on the West End in 2014. inevitably has more on his mind than spices. Suddenly the stage darkens on the palpable luxe, and in bursts Eddie (Stephen Hagan), an amputee ex-soldier who once worked as a decorator in this very household and has shown up with a score or two to settle, knives and a gun at the ready as needed.

Eager to extract a reckoning, at once moral and financial, that will help out his hard-working, stroke-ridden dad, Eddie is a one-man vigilante aiming to recalibrate the injustices of a society eaten away by greed. What is any person really worth? becomes the question ricocheting around the (spoiler alert!) soon-to-be-bloodied room – when, that is, Eddie isn't holding forth on both King Lear and the great Renaissance painter, Masaccio, and claiming "posit" as his favourite verb. 

At this point, you yearn for a plot twist – Gill and Eddie fall in love? – that might up-end the tendentiousness, given that Eddie's arguments amount to so much roaring to the choir. (How Hagan is going to safeguard his voice over the next few weeks is a separate issue.) But no: before long, the welfare of Gill and Hugh's son is factored into a pandemonium-rich finish that brings down the lights just as things get interesting: surely the real play lies in what happens next to this society in miniature whose gilded cage has been rattled for ever, not to mention to Eddie, who will presumably be sent to prison where he can spend his days swotting up on Descartes. 

The play's descent into brayng overkill is a shame, given a galloping if none-too-novel broadside that connects up to the realpolitik at large today, however much one nods in assent with Hugh when he derides Eddie's thesis-mongering as "simplistic". You have to credit Nunn, too, for engaging at this point in his global career with an Off West End playhouse to which he is a newcomer at age 77, and with a cast worthy of the National Theatre that Nunn used to run. But after a while, I'm afraid I tuned out of the repetitive and increasingly preposterous action and began pondering other possibilities, like what it might be like when some theatre impresario pairs Dessert with Moira Buffini's erstwhile National play, Dinner. Is there a script out there knocking around called Starter?

• Dessert at Southwark Playhouse until 5 August 
• More theatre reviews on theartsdesk