You probably remember the death of Gareth Williams - the GCHQ mathematician found locked in a holdall in the bathroom of his flat in London. Perhaps he was killed by the Russians; perhaps it was a sex game gone wrong. Or perhaps, as this masterful and engrossing script proposes, the truth is bleaker still.

Gareth Williams was a real person, with a real family, and some might question the propriety of entertainment so obviously based on his life and death. I’ll leave you to make up your own mind on that one - but at least Tom, the fictionalised version of Williams, is a likeable and relatable man. Guy Warren-Thomas ably embodies a witty but tragic character; gawky yet winsome, aware that he’s a misfit, entranced by a city where there’s “so much gay”. This probably wouldn’t end well for anyone, and in Tom’s case we know it ends very badly indeed.

Also in Tom’s flat is a man who goes by many names, but today introduces himself as Zac. The self-assured Zac is the opposite of the awkward Tom: confident in his sexuality, streetwise in his dealings, and certain in what he’s there to achieve. But behind the swagger Zac is a tragic figure too, and worse still, he knows it. Under Peter Darney’s direction, Max Rinehart finds a convincing balance between bravado and emotion, and - a few opening-night stumbles aside - confidently carries the weight of the storytelling as the unpredictable truth of his situation is slowly revealed.

It’s a wordy script, but pleasingly so, and playwright David Thame captures an enviable range of moods and styles. The more evocative passages - when Zac describes a landscape, or the people he spots at a party - have that special kind of lyricism that truly transports you there. The dialogue is natural and often quietly humorous, yet the undertow of menace never quite recedes. And while there are scenes here which could easily be cringe-worthy, in the event the sexual overtures between the men show the perfect balance of tenderness and tension.

A complex metaphor about quantum physics is an intellectual stretch - but if you invest the effort it takes to follow it, you’re rewarded with a fascinating perspective on the way that a chance meeting can fix the course of your life. But although I grasped the science bit, I didn’t quite understand why Tom has been targeted by the shadowy forces in play. Either the mundane reason we’re given is the true one - in which case a few earlier lines of dialogue don’t completely make sense - or we’re meant to take it as a kind of cover story, in which case there’s an extra layer of intrigue I wish they’d peeled aside.

On the night I attended, the opening felt a little flat, and the ending lingers longer than it really needs to. And while the story which unfolds is intellectually chilling, the visceral horror of the situation - the fact that there’s a body on the sofa - never quite pervaded my subconscious. So Kompromat still has a little room to grow, but there’s five-star potential here and I hope this talented team has the time and space to realise it. For now, I can recommend it as a fine, slow-burning thriller - and a near-philosophical contemplation on the dangerous allure of power.