Fifty years after In Cold Blood, we remain obsessed by true crime. Think Netflix's Making a Murderer or This American Life's Serial. Thebes Land takes aim at the form and shows - bit by bit, drip drip drip - how art gets in the way of the truth. It corrodes and mutates reality. It manipulates and corrupts.

T is a theatremaker; a playwright and actor. He had planned, he tells us, to put a patricide onstage at the Arcola; to bring a real-life killer face-to-face with an audience. It was all arranged with the Department of Justice and, in a metal cage, three metres high, in his grey prison tracksuit, sits Martin - a young man who killed his father with a fork.

Or does he? Sergio Blanco's play turns somersaults with the truth. It follows T's process – his meetings with Martin on the prison basketball court, his rehearsals with Freddie (Alex Austin), the actor now playing him – and charts the distortions that creep in en route. His notes on meetings are incomplete, and he smoothes Martin's words for flow, picks up on patterns and finds artistic allusions – to Oedipus, to The Brothers Karamazov, to Mozart and religious art.

At some point it gives way - is art leading or is truth? Martin's rosary changes from jasmine to rose and back, to suit T's purposes, but was there even a rosary before the write turned up? Was there a basketball court, or is that a reflection of T's own sporting father? Was there a Martin? Even his name is symbolic: of Mars, god of war. Freddie derives from peace. In time, nothing stands up.

Blanco's play is, in turn, translated and further twisted by director Daniel Goldman, who sews in local colour and culture. The only thing the playwright insists on, we're told, is one prayer (in French) and one piece of music. "The rest they can change." Can we even know Blanco's play – let alone ‘Martin's' ‘crime'?

What a sharp, satisfying watch this is – a play that runs rings around its audience; riddles us like the Sphinx did Oedipus. Scene by scene, it slips out of reach. Fiction slides into fiction, rehearsals corkscrew into ‘reality,' and come the end, nothing's solid. Blanco does for documentary art what Dennis Kelly's Taking Care of Baby did for verbatim work. It holes it below the waterline.

The cage, then, is clever. It boxes something up, pins it in place and, at the same time, disrupts our perspective on it. T doesn't just neatly package his subject, he both defines and exploits it and displays it at a distance. Blanco shows how art spins back on itself and shapes our view of reality. In doing so, far from being progressive, it simplifies the world and so maintains the status quo. T could help his subject, could educate or comfort him; instead, he appropriates his story for personal gain and self-expression. In our post-fact world, of liberal elites and press pens, Thebes Land is all the more chilling.

True, Blanco labours his point and risks overindulging it, especially since he has his postmodern cake and eats it, serving up the same salacious tittle-tattle he warns us off. For a play that points out the problems of art at length, and even suggests an alternative - art as education - but Thebes Land actively refuses to practice its own preaching.

Indulgence hardly impedes enjoyment, though, and Goldman's production is engrossing and slippery. It owes a lot to its actors: Trevor White, beautifully low-key as the flawed author, and Alex Austin, who carefully confuses actor and captive – one light, one dark, but both complex. True crime always is.

Thebes Land runs at the Arcola until 23 December.