Nicola Walker is simply magnificent in The Split: Barcelona

A beautiful young couple rushing headlong into marriage. A sun-soaked location. Romantic complications trailing the mother of the bride. There’s more than a dash of Mamma Mia! to The Split: Barcelona, the two-part special that picks up on BBC One a couple of years after Abi Morgan’s divorce lawyer drama came to an end – although given that our protagonists are a family of high-flying solicitors, everyone has considerably worse work-life balance than they do in Abba-world.

Indeed, the hustle never stops for Hannah Defoe, played by the magnificent Nicola Walker. She’s barely touched down in Spain before she’s fine-tuning the details of a prenuptial agreement, although this particular legal document is closer to her heart than most. Her daughter Liv (Elizabeth Roberts) is about to tie the knot with her boyfriend Gael (Alex Guersman), who happens to be the wealthy heir to a glorious Catalonian vineyard famed for its merlot and muscat. “Our contribution to this wedding will cover, at best, the patatas bravas,” quips Nathan (Stephen Mangan), Hannah’s ex-husband and the father of the bride, whose new tiny hoop earring seems to augur an impending mid-life crisis (it also provides a punchline for plenty of mockery from his in-laws).

Gael’s glamorous parents Valentina (Romina Cocca) and Alvaro (Manu Fullola) are keen for the bride and groom-to-be to secure their respective assets before walking down the aisle; Liv, despite having grown up in a home where marital settlements were discussed over the dinner table, sees the whole thing as depressingly unromantic. Oh, and the lawyer acting for Liv’s new in-laws? He just happens to be Archie (Toby Stephens), the charming bloke who Hannah met on Hinge, only to pre-emptively ghost him when she thought things were getting a bit too meaningful (she’s still haunted, it seems, by the end of her affair with former colleague Christie, and his subsequent departure for a new life in New York).

Safe to say there are zero boundaries between the professional and the personal here. Taking the beloved cast of a TV show to a balmy destination is a classic “spin-off episode” technique, and at first it’s not entirely clear whether The Split can thrive without spiky boardroom showdowns, power suits and shots of the London skyline. But any doubts in screenwriter Morgan’s ability to pull off this location and slight tonal shift are quickly dissipated. Subplots involving the younger Defoes are as deftly handled as ever. Rose (Fiona Button) is bristling at the responsibilities that come with her new life as partner to a vicar (Kobna Holdbrook-Smith’s Glen), while Nina is embroiled in a good-enough-for-now relationship with Julian (Tibu Fortes), whom her sisters brutally but accurately describe as “a very nice, boring man”.

The trio’s sibling dynamic is a delight, realistically but warmly observed. And Stephens slots effortlessly well into the world of The Split, where everyone is witty, emotionally vulnerable and has some kind of high-flying legal career. After the wrenching tumult of season three, it’s heartening to see Hannah spark with a love interest who seems like they might be worth her time. As ever, Walker’s textured performance is the main event here; she nails each gesture and expression, whether it’s a post-cava hangover grimace, a sympathetic eyebrow raise or a smile dampened with sadness. And when she inevitably switches into full legal mode as events go off the rails, she’s a force of nature. Walker is so good that she allows you to forgive some of the show’s more grating visual quirks, which are back here with a vengeance: the lingering close-ups of hands touching, the softly lit, slowed-down dancing filmed like a Center Parcs advert.

You get the feeling that Morgan has missed writing for these characters and brought them back out of love rather than obligation; there’s none of the perfunctoriness that hinders so many TV comebacks, more a sense of checking in with old friends. It’s a family reunion where all the jibes are good-natured, bubbling resentments are artfully defused and everything is suffused with a genuine affection – a true Christmas fantasy, then.