Annie Baker “Infinite Life”, National Theatre, Lyttelton

Sofi (Christina Kirk) is the youngest at 47, separated from her husband; she’s the narrative thread too. Nothing occurs without her on stage, so it’s not surprising she breaks out of role to announce the time lapses “eight hours… twenty-five hours” and so on. For once Baker’s privileging one character over others. But each character’s given a moment for witness and inwardness, reflecting on pain, sex and eternity. As Sofi notes: “like some punishment in a fairytale”.

Though it’s also how we accept and accommodate our broken humanity, and recognising our common frailty. In brief, being human with a dimmer switch.

Sofi’s also the most cerebral and in her later explicit directness and desires echoes the much younger Rose from The Flick. Alone she calls her husband Pete leaving searing voicemails, then the man whom she merely cheated with verbally by leaving explicit sexual fantasies: an update on the never-meeting epistolary couple in Under Milk Wood.

First there’s frail Eileen (Marylouise Burke, hypnotic as she winds out her fragile witness or takes offence, mildly to Sofi’s searing and vanishes). But adds laconically “This was the night you heard me screaming” before adding harrowing details. Yvette (Mia Katigbak) is maddeningly good at the relentless till she shows fragility behind the physical. Yvette over-shares – once litanically like a prayer – every ostis and itis, and its corollary: a pharmaceutical or surgical cure.

It’s when Yvette notes her cousin “narrates pornography for blind people” that opens up fissures as Ginnie says it’s “a generational thing”. When Sofi notes of her generation ”half the women I know watch pornography” – invisible boundaries are crossed. It’s a telling moment with the discovery of other people’s spaces; where this liminal half-world lulls you into thinking there are none; especially when you’re high on fasting.

Ginnie (Kristine Neilsen, a warm interposer) radiates sympathy and is first to help Eileen who stops dead for no reason. And explains Eileen’s Christianity to Sofi. It’s here Baker manages one of her lightning sketches on eternity. Ginnie’s own epiphany comes when she narrates the moment she realises through illness and pain she can’t have children. It’s like “shedding a skin… then I was fine.” Neilsen’s Ginnie sees in the round and cheerily hunts down gossip.

Though least elaborated, Elaine (Brenda Pressley) is Yvette’s obverse. Pressley brings out Elaine’s warm alertness to others’ hurt whilst also pointing up her fixation on organic cures and health as a moral imperative that cusps new-age exhortation. The kind that suggests if you’re in pain, you’ve asked to be ,but aren’t ready to hear it. Even here though, Baker pulls back: the suggestion’s muted.

This rhythm is mildly disrupted when Nelson (Pete Simpson, a hypnotic slow-burn) apparates. Sofi thinks she’s dreamt him till he returns; there’s instant chemistry. Nelson may charm but inevitably establishes his victim hierarchy of pain as greater than childbirth. They drift briefly over Eliot’s plot for want of small talk, but again Baker draws out their encounters to just two, where Sofi talks explicitly. Ultimately Sofi asks to see screenshots of Nelson’s colonoscopy: a corollary of his visual, her auditory approach to describing sex.

The denouement too – Baker fast-forwards in telegraphic moments – is quietly moving. Not overtly devastating, but in just a few revelations and physical moments Baker returns to her first two characters, Eileen and Sofi. A world of connection widens out of pain and ageing.  A hypnotic masterpiece affirming Baker as the finest American dramatist of her generation.