What If If Only review – Caryl Churchill's 20-minute play premieres at the Royal Court

Trust Caryl Churchill to pack more meaty matter into 20 minutes than most playwrights manage in two hours. Her surreal new short covers nothing less than bereavement, time and the universe – and does so with dizzying complexity.

I am never absolutely sure I grasp everything she is trying to say, but the sheer precision of her language and the originality of her thought always make me want to go on trying.

There's an example here, when a character called Someone (played with a thin-skinned transparency by John Heffernan) is sitting at a table set for one, talking to his loved one who has died, and listing the types of apple an artist could try to paint. "Did he specialise in a cox or a discovery or a russet or did he have a go at different kinds? Braeburn. Bramley. Winter pearmain."

The meticulous rhythm of that list – drawn out with relish by Heffernan – which is poetic and funny, absurd yet somehow touching, characterises the 83-year-old playwright's absolute mastery of her form. Like Picasso in his late sketches, she has become the essence of herself, still challenging, thoughtful and heading in directions no one else dares.
Someone's longing for contact with his vanished departed, its intensity recognisable to anyone who has suffered loss, conjures not her, but multiple visions of Future – all played by Linda Bassett in a loose green dress and Doc Martens. When she first appears – as a shadow on Miriam Buether's pristine set, perfectly lit by Prema Mehta – it does appear that perhaps she is a spirit from another world.

But she is something even less tangible: the embodiment of every kind of what if and if only, all the possible futures that may or may not include Someone's dear one. The future may be hopeful – "equality and cake and no bad bits" – or it may be terrifying visions of annihilation. In James Macdonald's carefully calibrated and absolutely focused production, Bassett embodies them all, with quicksilver turns of pace and tone, sometimes maternal, sometimes fearful, sometimes threatening.

She does this with apparent ease, an astonishing tour de force, full of consummate understanding and skill. The appearance of a small child (lovely, confident Jasmine Nyenya) offers a glimpse of hope, but Someone remains trapped in his own wistfulness.

The play seems to be about the necessity for acceptance, about the metaphysical need not to long to change the unchangeable, but also a plea for awareness of all the horrible outcomes that the world may face. It seems to ask for us to live in the here and now, to alter what we can for the sake of our youngsters. But it also encompasses much else.

It's that elusiveness that makes Churchill such a rewarding writer. You can buy tickets to watch this, early and late, alongside Aleshea Harris's Is God Is which would make for an evening of soaring female writing. But it is also quite substantial enough to stand alone, a rocket of thought to propel you into the night.