A handful of British astronauts, sealed in a research station on Pluto, wait for contact from a blighted Earth.

And wait.

And wait . . .

And when their clocks begin to glitch, they can no longer even be sure how long they've been waiting.

Science fiction is so rare in theatre that it feels striking and satisfying to discover it can be done at all. I expected that it would be difficult to enter into agreement with the play's pretense that actors only meters away were really stranded on the edge of the solar system. It's largely a testament to Merle Hensel's superb set that X clears this barrier easily. From the moment the lights go up to reveal the subtly askew interior—walls of stark metal panelling, a window opening onto blackness at the rear—suspension of disbelief is effortless. That is, at least so far as the setting goes. When it comes to the psychology of the crew, X is never quite as persuasive.

Despite the rarity of finding astronauts at the theatre, X isn't the first play to take inspiration not from the boundless possibilities of space, but from the sealed-in claustrophobia of space travel. David Greig's The Cosmonaut's Last Message to the Woman He Once Loved in the Former Soviet Union revolves around the plight of a pair of lost spacemen, drifting in a space station above the planet that had forgotten them. Both plays necessarily concern loneliness and isolation, and both are non-linear and elusive, but The Cosmonaut's Last Message is interested in the thwarted desire for connection, in unheard speech and longings unrecognised, while X is concerned with the ruthlessness of time, which inexorably strips hope and sanity both from its characters and from the planet they left behind. "X" symbolises time in the mathematician Cole's calculations, but it's also a wound, a kiss, a placeholder, the sign that marks the spot . . .

However, the metaphorical freight of these and other motifs are never very satisfyingly explored. The play is frustratingly apt to gesture towards meaning whilst refusing to actually get up and travel towards it. It invokes images that could be symbols without convincingly investing them with symbolism. There are moments that are startlingly effective—but moments they tend to remain, scattered dots rather than a line.

The effect is one of fitful bursts of power. After a glacial start—notable mostly for the depressing revelation that even after the last bird has died and the last tree has fallen, men will still not stop talking over women—the rather thinly sketched characters begin to crack under the weight of their monumental isolation. Ray, the captain, begins to talk of something in the blackness; there are Waste Land-like hints of one more crew member than can be counted. Then, one by one, the crew start to vanish as if in a futuristic reboot of And Then There Were None. It's in this gradually accelerating breakdown that X is at its strongest, drawing as much from films like Event Horizon as anatomies of waiting like Waiting for Godot. If the play's sense of gathering dread is frequently deflated on the way to crescendo, still there's enough by the end of the first act to fuel a genuinely nightmarish climax. This is probably the play's strongest moment (and I'm therefore reluctant to spoil it); yet even here, there's a nagging sense that the shock has only been partially earned, and that its impact is largely derived from transplanting rather elderly horror film tropes to live theatre.

In the second act, I began to find myself perversely reminded of an old sketch by Stewart Lee and Richard Herring. Lee's Jesus is delivering a parable to his disciples, but whenever Herring's Matthew attempts to unpack one of his metaphors Jesus forestalls him with a beatific "Ahh!" "No!" insists Matthew at last in frustration, stubbornly trying to pin down what is actually being said. "Not 'ahh!'"

On any literal examination of its plotting, the play seems to resist such questioning. Indeed, it must—for its premise won't stand much inspection. If plants and non-human animals have entirely died out on Earth how can there possibly be the resources to supply the team with apparently infinite food supplies on such a distant world? Ray, the captain, grumbles that the mission is a throwaway, "a tax write-off"—how could an apocalyptic Earth still be functional enough to manage taxes, let alone a pointless trip for a neurotic crew "to study rocks" billions of miles away? It's vaguely suggested that the expedition is something to do with attempts to abandon Earth and colonise space, but how this particular crew could possibly serve such a purpose is never addressed. But as the narrative chops back and forth in time and whole scenes are revealed not to have "really" taken place, the play retreats from this kind of scrutiny—perhaps it's all not literal. Perhaps this is not "really" about astronauts on Pluto at all. Perhaps the details don't matter ("Ahh!").

But then what does? For it's not only on the level of the plot and premise that X is so slippery as to leave doubts that there's anything there to grasp. As the characters fall apart yet further, I began to wonder: is disintegration meaningful without something solid to disintegrate? Is the fact of disintegration—that it's possible to say "this is a play about disintegration" (of sanity, language, time)—enough? Or is this too a gesture, without some sort of verisimilitude in collapse? What is X actually saying about disintegration? That minds do break—that minds in this setting would break—is undoubtable. And yet I was only intermittently convinced that minds break like that.

Would a small group with no one else for company or stimulation really forget their own, and each other's, names? Would they re-enact each other's delusions? Would they lose, and then abruptly regain, their short-term memories? Would they really hallucinate whole backstories, relationships, and job titles for characters who probably aren't there? And would a team of scientists give up so rapidly on even trying to resist their unravelling? For while I found the impermeable pluckiness of Matt Damon in The Martian grating, I longed for just a fraction of his can-do spirit for this woebegone lot. Even the most optimistic of them has no suggestions beyond a more cheerful passivity. The clock, apparently, cannot be mended. No one in the team of scientists tries to create any new system for marking the passage of time—Pluto does orbit the sun, they could surely see the stars. When the computers fail (leaving the life support intact) no one thinks of writing their slippery memories down on paper, or on the walls. Humanity may be extinct on Earth but Mars, we are told, is "full of blond Americans." No one tries to contact them. No one even seriously considers walking out of the airlock.

And yet, again, the play passes through a strange catharsis where even its very frustrations seem to break down into something else. "X, X, X" two characters chant at each other, stumbling across the stage, in a kind of aphasic frenzy. It's at first strange, then irritating ("yes, but why would they do this?" "Ahh!"). Then at last—powered by the actors' conviction, Vicky Featherstone's impressive direction, and some astonishing light-work by Lee Curran and Tal Rosner—compellingly frightening.

Then, a degree of coherency returns, and perversely, the play seems on shakier ground again. The narrative enters a series of twists—difficult to pull off for all but the most tightly plotted work, let alone the loose and baggy X. A character is not who we thought. It's next to impossible to square this revelation with earlier events—and harder still to find the connection between two personae which appear to have nothing in common. Does it matter? If the play—perhaps, perhaps not—evokes a dying mind's jumble of memories, does it matter if some of them are scenes the character could not have witnessed?

Ahh.

Some will doubtless see more in X's evasions than I did. For my money X—probably—has some interesting elements bouncing around inside its airlocked walls, but in the end, puts disappointingly little energy into making anything substantial of them. The innovative staging, however, keeps this mission to Pluto from being wholly wasted.

Sophia McDougall is the author of the Romanitas trilogy, set in a contemporary world where the Roman Empire never fell, and two novels for children, Mars Evacuees and Space Hostages, about girls, boys, and fish-shaped robots. Her short stories have been published by Jurassic Fiction, Solaris, and NewCon press. She also creates digital art and mentors aspiring writers.