It can be difficult to remember that Tennessee Williams, the great songster of the Deep South during the 1950s, was still churning out plays when he died in 1983. In the 1960s he was past his peak and he began to experiment with form, perhaps hoping to compete with fashionable youngsters like Tom Stoppard and Harold Pinter. Hampstead Theatre staged the world première of his absurdist melodrama The Two Character Play in 1967. And now, a mere 54 years later (an interlude that hints at its merits as a crowd-pleaser), the show has returned to its cradle. Sam Yates directs.

This is an obscure and sometimes baffling script that features some excellent innovations and ideas. It opens as a backstage drama between a brother and sister, Felice and Clare, who are actors appearing in a ramshackle thriller. The cast and crew have gone missing. Even the script is incomplete. Felice and Clare go ahead with the show despite their fears that disaster looms. Clare tells Felice that when she plays C-sharp on the piano she is indicating her wish to add supplementary material.

The action then shifts to the thriller itself which is a classic Williams play. Two siblings are trapped in their Midwest home after their parents were involved in a murder-suicide. They cower in their sitting-room, peeking out through the windows, and imagining that hostile notes are being pushed under the door by angry neighbours. This set-up is funny, dramatic and unpredictable. Clare plays C-sharp on the piano and invents a new speech. But her effort knocks Felice off his stride and so he plays C-sharp as well and improvises his own new material. They compete to reel off chunks of unrehearsed dialogue. At last, Felice shuts the piano lid and sits on it. No more improv, thanks. This scene works because the actors don’t know whether they should try to co-operate in a credible performance or just sabotage each others’ efforts. The enjoyment continues when Felice raps his knuckles against a wooden upright and claims that the neighbours are banging on the door. This entire routine could have been performed brilliantly by French and Saunders or by Morecambe and Wise.

But the enjoyment peters out and the play becomes indecipherable and self-involved. Dramatically it can’t go anywhere because Felice and Clare are brother and sister, just like the characters in the Midwest drama. There’s no hope of escape or development for anyone here. This is a decent production of a little-known play but the audience will be limited to hardcore Tennessee Williams fans. At a time when our theatres are trying to bring audiences back they should avoid high-minded obscurantism.

Southwark Playhouse has the right idea with their new show, Operation Mincemeat. This is one of the most successful knock-off jobs you’re likely to see. Everything is nicked. The musical rhythms and the syncopated lyrical style are straight out of Hamilton. The plot is a hoary old number from the second world war. And the liberties taken with British history are reminiscent of the hit show Six.

The action takes place in 1943 at the Special Ops department where a gaggle of boffins, spies and crazies are cooking up clever ways to defeat Hitler. A shy brainbox named Cholmondeley hatches a scheme to convince the Germans that the Allies are about to invade Sardinia. This will lead to the transfer of troops out of mainland Italy which will then be vulnerable to attack via Sicily. A macabre subterfuge is proposed. The body of a drowned RAF commander is to be dropped off the coast of Spain along with ‘secret plans’ outlining the Sardinian invasion. Enemy agents will stumble on the counterfeit documents and their discovery will prompt the Germans to evacuate Sicily and leave it at the Allies’ mercy.

The show follows the British spies as they search for a suitable corpse and invent a back-story for the non-existent RAF commander. Their orders are to write a love letter from the officer’s sweetheart to be placed in his uniform pocket. The spy who pens this letter is a widow whose husband died at Flanders and her composition becomes a deeply personal confession of the unspoken feelings that have tormented her for years. It’s an unexpectedly heartbreaking moment (borrowed from a similar letter-scene in Rattigan’s war-time classic, Flare Path). These emotional highlights are varied with broad comedy routines and displays of raunchy cabaret where the cast put on slinky costumes and high-kick their way around the stage. This terrific show has one key advantage beyond its memorable title, its upbeat script and its superb cast. It’s inexpensive. There are just seven members of the company, and the simple set will be easy to relocate. This production has a heart of gold. West End impresarios should check it out immediately. It’s a contender.