"The Party Girls". Oxford Playhouse

It's Sisters Week at the Oxford Playhouse. While the Brontës are dying of consumption in the Burton Taylor Studio at the back of the building, the Mitfords are going full Adolf in the main house.

The British have an abiding fascination with the Mitford Sisters. They’re like monsters in debutante form, Frightening Young Things. Buried barely 18 miles from the Playhouse Box Office in the chocolate-box village of Swinbrook, pretty graves all in a row, they are proof that some corner of a British field is forever fascist.

We just can’t get enough of them. There are at least thirty books that tell their story, from the Collected Letters to Hitler’s Valkyrie. As recently as this summer, TV audiences have been treated to Outrageous, which explores the lives and loves of this bizarre family. But Amy Rosenthal’s new play wisely avoids tackling the whole saga, and focuses on the heroic Jessica (Emma Noakes in a performance oozing dignity and wit), who revolted against the family tradition of right-wing extremism and became a campaigning socialist – even marrying a Jew, which can’t have gone down well with the in-laws.

The play is composed of selected scenes from the lives of the sisters, ranging from 1932 to 1969. Again like Jane Eyre next door, it jumps backwards and forwards in time, comparing outcome with intention, and youthful potential with dying pain.

Rosenthal’s writing echoes across the decades with lost ambition, regret and bitter idealism. Each of the sisters fights her own corner with the vibrancy of total self-belief and centuries of privilege. And somehow, Rosenthal even imbues the fanatical extremist Unity (truly more of a Hitler Girl than an It Girl) with moments of poignancy. At one stage she sits in the window yearning for the Führer while tugging forlornly at a plucked flower. When rebuked by Nancy for damaging it, she says, ‘It was only the leaves, not the petals’, and the hopelessness of her delusion feels tragic.

At the climax of the play, in 1969, an aging Jessica confronts Diana (who married Oswald Moseley and actively supported the British Fascist Movement) and begs her to admit that she was wrong. Diana gives not an inch. Instead she pointedly looks to the future and tells Jessica that antisemitism will have its day. (For a truly chilling listen, I recommend searching for the Diana Mitford Desert Island Discs on BBC Sounds. Sue Lawley also probes her fascist history, and the elderly Duchess is unrepentant to the end.) Prejudice is inherited, and the takeaway from this play is about the effort needed to escape family influence.

Despite the lyrical writing and a group of impeccable performances, The Party Girls does drag in places. 90% of this play is stasis filled with discussion. Rosenthal is aiming at a Three Sisters vibe with a Mitford skin. But she is no Chekhov. His ability to convey exquisite pain masked by everyday pleasantries would be ideal for the Mitfords, but the chit-chat here frequently conceals rather than reveals the inner lives of the characters. Consequently there are longueurs where the party girls are more dreary than sparkling. And while their voices and language are brilliantly observed and convincing, the debate they have feels like what it is: a debate. It’s on the surface, like an episode of Question Time, rather than submerged and resonant. Consequently, when Unity (spoiler alert but it’s a well-known fact) pulls out a gun and shoots herself in Munich, it comes out of nowhere.

The play looks gorgeous, with a wafting, diaphanous gauze of dark blue satin whisking aside for each scene, as if offering us a glimpse behind one of those stunning 1930s ball gowns. And with a minimum of fuss, Simon Kenny’s sparse design conjures the kitchen of Asthall Manor, a back alley in New York, the English Garden of Munich, and a posh apartment in Versailles, while lightning costume changes fling the sisters from youth to age and back again in seconds.

If The Party Girls is a collection of scenes from the lives of interesting people, it doesn’t always pick the most interesting scenes. But it has a true purpose, it is full of heart, and it directly addresses one of the key issues of our day: how do you talk to family members with whom you profoundly disagree? In a way, maybe we’re all Mitfords.