Best Interests review: Unflinching Sharon Horgan drama imagines parents’ ultimate nightmare

Michael Sheen co-stars in Jack Thorne’s BBC One series about a couple driven apart over whether to stop treatment for their daughter

Watch enough TV, and you’ll find yourself put through the emotional wringer like wet Victorian laundry. At times, it feels like every trauma of the human experience can – and must – be brought to vivid life for small screen audiences. Illness or abuse, grief or depression, violence or neglect: you don’t have to leave your living room to run the gamut of psychic wounds. And so, it was with a huge sense of trepidation that I pressed play on BBC One’s new four-part drama, Best Interests, which fictionalises the ultimate nightmare, skulking in the back of every parent’s mind.

Nicci (Sharon Horgan) and Andrew (Michael Sheen) have two daughters: reserved trumpeter Katie (Conversations with Friends’s Alison Oliver) and perpetually upbeat 13-year-old Marnie (Niamh Moriarty), who has an atypical form of muscular dystrophy. The nuclear family’s lives in suburban Cheltenham revolve around Marnie’s care, an orbit that is thrown when a chest infection sends the youngest daughter to the ICU. There, they receive the dreaded news that they’ve spent a decade anticipating. “We think it’s time to discuss whether it’s right to keep treating her,” comes the verdict of Marnie’s doctor Samantha (Noma Dumezweni).

Cue a splintering within the tight-knit family. Nicci will do anything to maintain Marnie’s treatment regimen, while Andrew gradually loses faith that this is a winnable battle. “Promise me you’ll fight for her,” she implores him. “I will fight with everything I’ve got,” he replies, but increasingly they seem to be flying the flags of two different causes. Horgan’s Nicci is powerful, in a brittle way, and entirely convinced of her sole priority; Sheen’s Andrew, conversely, is equivocal, drawn to a more cautious judgement. As a two-hander, they are terrific, both wholly believable in their frustration and grief. Oliver too gives a stellar performance as a teenager dealing with being overshadowed by incipient mourning, and Moriarty (who has cerebral palsy) is a revelation as Marnie.

Of course, the acting is only one part of the puzzle, and projects like this require a real delicacy to the script. Writer Jack Thorne’s oeuvre (ever expanding – he must be one of the most overworked men in British television) is hit and miss: for every critically acclaimed show like The Virtues there’s a dud like Kiri. Best Interests draws heavily from the much-publicised case of Archie Battersbee, whose parents fought a lengthy battle to prevent his life support being switched off. And it manages to straddle its difficult line. Even the intrusion of a Christian support network is handled sensitively. “This is about establishing that medicine is about opinions, and not just facts,” Brenda (Lisa McGrillis) tells a progressively desperate Nicci. Only the transplantation of the story to a middle-class family in the leafy Cotswolds feels like it has been done for the comfort of the show’s audience. The rest is faced with unflinching candour.

As the story develops, it moves away from being a claustrophobic family drama, and becomes a broader, more searing, portrait of the influence of the press and social media. Always the question remains: what’s in Marnie’s best interests? The final instalment in the quartet, which plays out as a courtroom drama, lacks something of the vital intimacy of Best Interests’ early moments. But the writing is humane throughout, managing to stay witty and lively, even as the gut-wrenching power of the story encroaches. This is not a show to watch with full tear ducts (have a good cry first or, like Marnie on her first date, you’ll ruin your make-up).

“There are many beautiful stories in this life,” a paediatrician (Kevin Eldon) tells the family at their first consultation with baby Marnie. “Please don’t assume that Marnie’s story is going to be any less beautiful: it’ll just be different.” Keeping that beauty in a story like Best Interests is no mean feat. The show poses big questions, both about the practical issues surrounding end-of-life care, and more philosophical enquiries about the value we, as a society, place on young lives. Anchored by a raft of excellent performances, this is a powerful, moving story of the impossible decisions facing the parents of seriously ill children.