ore than three months after UK theatres were closed by the pandemic, it is both poignant and uplifting to watch actors walk back on stage. Just about keeping a metre apart, Matt Smith and Claire Foy have returned to London’s Old Vic for a handful of physically distanced performances of Lungs, resuming roles they played in 2019. This time, however, the auditorium is empty and the audience on Zoom. Duncan Macmillan’s nimble play, about a couple anticipating parenthood, suits this streaming experiment directed by Matthew Warchus, the first in the theatre’s In Camera initiative. It’s a two-hander, so there’s no supporting cast to swerve, and the script specifies no costume changes, props or interval. Lungs was written for a bare stage. The effect can be especially immediate and communal: my memories of Paines Plough’s 2014 in-the-round production are indivisible from the presence of other audience members huddled inside the Roundabout venue. The play is an appropriate choice in content as well as form. The couple – named W and M – consider the ethics, emotions and economics of having a child, and the personal and planetary consequences. Their arguments resonate during lockdown, which brought predictions of a baby boom quashed by research suggesting couples are delaying parenthood due to pandemic-induced anxiety and recession. The climate emergency weighs heaviest on Macmillan’s couple. In a play packed with funny exchanges, one of the best is Foy’s horrified estimate of a child’s carbon footprint: “10,000 tonnes of CO2. That’s the weight of the Eiffel Tower. I’d be giving birth to the Eiffel Tower.” Warchus, an incisive director of film as well as theatre, presents the story in split screen. Smith and Foy occupy the same stage but rarely the same shot. It’s jarring at first but accentuates Macmillan’s interest in what is shared and what remains separate in coupledom. It also emphasises the lines about distance and disconnect. When M struggles to fathom what W is saying, she wryly observes, “You’re buffering” – a remark that gets an extra laugh on Zoom. Occasionally Macmillan’s satire of their over-thinking threatens to make the couple emotionally distant to the audience, too. Some split-screen compositions work better than others: the couple sit as if back to back, their partially seen bodies are aligned to create one whole and, most successfully, the cameras zoom out to make them tiny figures contemplating their positive pregnancy test, fragile in the flush of an unknown future. This is all exploratory use of a new medium, and a refreshing contrast to pedestrian archive streams of stage productions. Smith and Foy will give several performances, rather than filming a single one, so the initiative preserves the notion that each night a play takes on different colours. But replicating the Old Vic’s 1,000-audience capacity means the online run has sold out when it deserves a wider audience. Foy and Smith are superb as the couple whose comfortable ease disguises an empathy shortfall. Smith is the languorous musician who watches on, bemused, after raising the baby question on a trip to Ikea. Foy is the PhD student who foresees a whirligig of vomit, birthday parties and Beatrix Potter. She frantically rewinds through her ancestry and fast-forwards to the child leaving home and hating them. The play, aided by Macmillan’s propulsive dialogue, similarly leaps through the couple’s relationship with conversations jump-cutting across days and years. We see a familiar pregnancy inventory – peeing on a stick, scans, first awareness of a bump – and the couple’s what-if questions still prickle. Macmillan captures the collision of racing thoughts about the future and hyperawareness of the present moment that you experience on the path to parenthood. He earnestly asks, amid the middle-class satire, the question that ends his climate-change play, 2071: “What kind of future do we want to create?” Lungs: In Camera runs online until 4 July.