For the many Patsy Ferran fans, of whom I count myself as one since she burst onto the stage in 2014 with a scene-stealing comedy performance as the maid alongside the great Angela Lansbury in Blithe Spirit, this is the actor as you will never have seen her before.

The promise of that debut was fulfilled four years later in the Almeida’s revival of Tennessee Williams’s Summer and Smoke in which Ferran played Alma, the prim daughter of a minister who falls for bad boy Johnny, son of the town’s doctor.

Ferran’s Alma was a tremulous, twitching wren wracked by disabling self-doubt through which a steely strength of character eventually emerged. She deservedly won many awards for the performance and a similar transition can be seen here in the UK debut of Bess Wohl’s two hander. Set just before the Second World War in an American summer camp run exclusively for youth of German descent, Ferran plays unnamed teen Her opposite Luke Thallon’s Him.

Wohl discovered the history of the camp while staying with her family in the Long Island town of Bellport, not a far from Yaphank where the camp was sited. After discovering that the area was a self-imposed Germanic ghetto, in which Nazi ideology had taken hold to such an extent that one of the roads was called Hitler Street, Wohl wrote the play in the teeth of the pandemic while Donald Trump’s reelection campaign was in full swing.

Sure enough the phrase “make America great again” rings out during the show’s 90 uninterrupted minutes — a knowing reference to the wave of neo right-wing sentiment that if many of the 75 million voters who voted for Trump had had their way would have kept him in power despite losing the election.

Yet after establishing the power of popularism, the play becomes unsure of where to go narratively after making its point. Still, getting to the apex of that moment is captivating, thanks largely to the performances of these two terrific actors.

Thallon plays an all-American Ubermensch, a blonde poster boy for the ideology being instilled by the camp’s (unseen) organisers. As strong as he is socially awkward his nervous energy around girls is shed with an axe as he chops wood brought to his block by Ferran’s diffident new arrival. They fall for each other in the uncertain, emotionally messy way teens in the grip of sexual awakening do (or did), but it is the transition of Ferran’s character that is so gripping. At first sceptical of simple-sounding ideas that have gripped her new friend (everything that is best in the world is German) it emerges through the later scenes that she’s a quick study when it comes to learning German.

Her rise is rewarded with the job of delivering a speech to the camp and is here that Ferran’s character haltingly then with certainty delivers a speech modelled on the delivery of Hitler himself.

It is an incredibly potent moment in which the girl is subsumed by the hatred flowing through her veins. Jews must be crushed; their cries for mercy ignored, and then in the flush of of approval from an audience of 40,000 the transformation is complete, her Ubermensch now a mere disciple.

The moment is superbly realised in Katy Rudd’s simply staged production. But the subsequent attempt to add a note of complexity in which Ferran’s character speaks of an experience of clearly Jewish humanity, feels like a flagging of Wohl’s good intentions rather than a compelling coda to her play.