A world without religion might sound like a dreamy John Lennon lyric, but it’s a brutal reality in Bag of Beard’s unsettling thriller The Messiah Complex. A hundred years from now, the “Great Experiments” have determined that God cannot exist, and any display of faith, fiction or indeed anything that can’t be scientifically proven as fact, has been declared illegal. This is a problem for lovers Sethian (Anthony Cozens) and Sophia (AK Golding), who refuse to give up their faith despite the constant threat of punishment. Sethian’s devotion to Sophia, and Sophia’s to their mysterious leader “Adam”, set in motion a chain of events that ultimately leads to Sethian’s incarceration, where the Nurse (Sasha Clarke) will seemingly try anything to convince him to renounce his beliefs.

The play jumps back and forth in time between now and then, and sees Sethian caught in the middle between two extremely opposing views. Will he break under the Nurse’s regime of psychological and technological warfare, or will he remain true to Sophia and her equally unpredictable methods? And more importantly, do we want him to? Nothing is quite as it seems in this world, and our assumptions and sympathies will be challenged over the course of the play’s 70 minutes, leaving us feeling more than a little uncomfortable and with many more questions than answers.

Whatever we might think about the subject matter, which is not for the faint-hearted (check the long list of trigger warnings in the programme before entering), there’s no denying the quality of the production, which was devised, scripted and directed by Alexander Knott, James Demaine and Ryan Hutton, with additional devising by the company. Video projection gives the piece a cinematic feel and, even before the show begins, adds to the unsettling atmosphere that pervades the space. Dramatic use of lighting at key moments keeps us on our toes, and the introduction of a microphone is an interesting twist, reinforcing the idea that both women are preaching their own beliefs to an audience – whether or not that audience is willing to hear what they have to say.

The acting too is excellent. In a play that’s about the power of language, all three deliver their lines to perfection. AK Golding has a soothing, persuasive voice; even if we don’t really follow what Sophia’s talking about much of the time, we want to believe her. Sasha Clarke’s Nurse, in contrast, adopts a much crisper, more authoritative tone which slips only occasionally to show us the real person – a former colleague of Sethian’s – behind the zealous conviction. And at the centre of it all is Anthony Cozens, who is astonishingly good as the conflicted Sethian, his emotional and physical torment almost visceral as he wrestles with the choices others are forcing him to make.

The Messiah Complex is not the sort of play you can watch, then go home and immediately forget about. It’s thoughtful, haunting and at times downright disturbing. Different people will no doubt interpret it in different ways; I’m still figuring out what I think it all meant, and will probably continue to do so for several days. It asks questions we might prefer not to answer, and challenges assumptions we didn’t even realise we’d made – and while that’s not always a comfortable experience, it’s also a sign that we’re watching intelligent and potent drama. Go and see it… but don’t expect to sleep particularly well afterwards.

The Messiah Complex is at Vault Festival (Network Theatre) until 19th March.