Martyr, Unicorn Theatre

Following a dangerously selective reading of a religious text, 15-year-old Benjamin has adopted a fundamentalist doctrine that espouses misogynist, homophobic and puritanical views and, at its extreme, violence. Neither his mum nor his teachers know how to handle him. The clever twist in Marius von Mayenburg’s 2012 play: that text isn’t the Qu’ran, but the Bible.

This change in faith revitalises the oft-repeated concerns dominating headlines and opens up the debate to extremism in all forms, with militant atheism taken to task alongside Benjamin’s (Daniel O’Keefe) hardline Christianity. Biology teacher Erica (Natalie Radmall-Quirke, pictured below with Mark Lockyer and O’Keefe) deliberately – and fruitlessly – positions herself as an opposing force, while the neoliberal headmaster (Lockyer) goes too far in the other direction by airily tolerating his radical student’s intolerance. If the play, crisply translated by Maja Zade, is short on solutions, that’s because we’ve yet to formulate a coherent response.

Benjamin’s zealotry begins with the demand that female students don more modest apparel in swimming lessons. It’s not a move calculated to win him many friends, though he does pick up an “apostle”: disabled, bullied George (Farshid Rokey). Soon, Benjamin’s objecting to the teaching of evolution by donning an ape mask, stripping naked to protest a condom demonstration, claiming he can heal George, and plotting revenge against those who stand in his way.

While the religious escalation is clearly presented, the psychology behind it remains murky. Erica theorises that he’s overwhelmed by his changing body – “Puberty is a form of temporary insanity” – and sees God as a comforting parental presence, perhaps replacing his absent father. There are also hints of sexual fear and confusion, with Benjamin rejecting the advances of a female classmate (Jessye Romeo) and unable to read the subtext of George’s attachment to him. But van Mayenburg seems more interested in the dialectical argument than the people voicing it.

Tonal oddities make the piece an awkward bridge between Brecht and CBBC. While the younger characters are portrayed relatively naturalistically, Lockyer’s head is bizarrely chauvinistic and inappropriate – a cartoonish echo of the sexist slant to Benjamin’s faith. Flaminia Cinque’s harassed mum is only capable of blunt overstatement and Kriss Dosanjh’s vicar essentially acts as a prop, while Erica’s obsessive response is never given credible underpinning. An overblown climax, featuring a literal crucifixion and deathbed confession, swaps creeping, believable horror for safely distanced melodrama.

Still, a committed O’Keefe (pictured above) and Radmall-Quirke bring heat to their conflict, Brian Lonsdale provides welcome comic relief as her bumbling boyfriend, and Rokey’s matter-of-fact George is warmly engaging. Ramin Gray’s well-intentioned touring production is constricted by its flat-pack set, with the constantly onstage cast jammed between desks, benches and a paddling pool. Needs more coherence in approach and firepower in telling, but a commendable representation of a vital debate that should resonate with viewers of all ages.

• Martyr at Unicorn Theatre until 10 October