Crushed Shells and Mud (Southwark Playhouse)

Ben Musgrave won the very first Bruntwood Prize with his debut, Pretend You Have Big Buildings. For whatever reason, he has never broken through and, a decade on, his latest still feels promising, without actually coming together: interesting ingredients made into something soupy.

Awkward soul Derek (Alex Lawther) spends his time in a run-down mobile home on the coast, a wasteland den of sorts. He writes there, or sits on the roof and stares dreamily out to sea. When Lydia (Hannah Britland) turns up, seemingly for the holiday season, he falls for her unaffected ease, only, as is so often the way, she’s more attracted to the laddish Vince (Alexander Arnold). "It’s a mistake that awkward, shy boys have made throughout history."

What looks like a teenage romance, however, slips out of its genre. When Lydia cuts her finger, she freaks out. Nor will she snog Vince. Derek spots her shooting a jab into her arm – a sure sign that she’s carrying the infectious disease that has swept and all but shut down the country. Sure enough, Peter (Simon Lenagan), a member of an organisation seeking to out sufferers in hiding called The League, is soon sniffing around.

Crushed Shells and Mud conflates the imagery of contagion and immigration – HIV on one side, EDL on the other – drawing out the fear that underpins hate. Infection might threaten one’s life, but immigration, so the argument goes, threatens one’s livelihood. Musgrave, quite cleverly, snips race out of the equation.

There’s more than that, though, and Musgrave never pins his symbolism down pat. He’s concerned for youth, with all three teens hampered somehow: Lydia, with the disease; Derek, with his oddity; Vince, with his unhappiness, triggered, we’re told, by his father’s behaviour towards him. In an overgrown, unkempt Britain, the play advocates kindness, care and, in time, courage.

It is, really, a six-part sci-fi drama in want of a Channel 4 commission. You feel shortchanged by seeing this national, possibly global, crisis through a single incident, but, at the same time, its carefully drawn characters are swamped by the scale of events. You could quite happily watch the teenage tussle over Lydia without any notion of contagion or catastrophe.

That’s what Musgrave writes so beautifully: these intricate, intimate moments – psychological dances of persuasion, rivalry and cruelty. Vince, not taking no for an answer, wheedles a kiss out of Lydia; Derek, wounded by rejection, snaps to an act of betrayal; Lydia trying to conceal her disease beneath a smile. They are played beautifully too: Lawther, who played the young Alan Turing in The Imitation Game, is sweetly gawky; Britland is breezy, perfectly cast and Arnold, best of all, manages to be both vicious and vulnerable.

In time, however, the play’s world starts to fracture under the weight of unanswered questions and inconsistencies that even Russell Bolam‘s loving production can’t quite smooth over – and nobody does dystopia on the small-scale better than Bolam.

Crushed Shells and Mud runs at Southwark Playhouse until 24th October.