In a café in Cold-War-era Budapest, a potential Soviet mole meets a bashful British spy. He’s a first-time handler, it turns out – and she’s a first-time agent too. But is this furtive assignation a defection or a date? The question hangs over the start of A Covert Affair, a gently witty rom-com which turns into a high-stakes thriller.

I’m not spoiling anything if I reveal that the naïve Englishman is being played: we can clearly see it, and on some level he must know it too. In one of the most entertaining scenes, we listen in on parallel debriefs with MI6 and KGB supervisors, learning how similar the two sides’ objectives are yet how differently they plan to achieve them. Some gentle wordplay results from the Soviet woman’s imperfect English, and there’s visual humour too, most notably when the British agent holds forth on professionalism while singularly failing to eat a crab.

Unfortunately however, the performance space has neither raked seating nor a raised stage, and much of the play is performed sitting down. From my position three rows back I could rarely see both of the actors, and one crux scene effectively became a radio play for me. It’s unfair to blame a production for the weaknesses of its venue – but it is reasonable to expect some adjustments in response to the space, and in this case the faults are too significant to ignore.

The tone becomes darker around the midway point, as the consequences of ill-considered bedroom talk suddenly become very clear. Alex Macfarlane and Charlie Turner’s script manages the transition well – again hinting that the two sides are united in approach, if not in ideology. I didn’t feel the tension and danger as strongly as I’d have liked to, but the shifting power-play between the agents and their agencies is nicely realised, and the dynamic between the two central characters evolves credibly too.

Some plot points stretched credibility – it felt odd that these two people, ostensibly betraying their countries, would do so on full show in a restaurant – and a few lines were inaudible to me. But Turner has the persona of a British innocent abroad down to a (weak milky) T, while Ella Sheree as the gutsy young Soviet projects a convincing mix of determination and fear. Overall, despite a few issues to be ironed out, this affair won’t stay secret for long.