"Middlemarch". Swan Theatre, Stratford-upon-Avon

Short books can be wrecked by overlong adaptations (see The Hobbit movies), and long books can be ruined by overshort ones (The Bonfire of the Vanities). But the Royal Shakespeare Company’s time-honoured technique of splitting weighty Victorian novels into two parts is a winning formula. It worked magnificently last year with The Forsyte Saga, and it works almost as well with Nina Raine’s adaptation of George Eliot’s masterpiece, Middlemarch.

The Forsyte Saga found one clear line through John Galsworthy’s five books, and wove it into a day of theatrical inventiveness that – crucially – didn’t feel like an adaptation. Middlemarch is more sumptuous. Longer than Forsyte (seven hours as opposed to five), it feels closer to its original material. This is both its strength and its weakness.

Strength, because it’s a rich, immersive tapestry of fascinating characters, intriguing sub-plots and showpiece scenes. Weakness, because it never quite breaks the shackles of its literary source.

The story is a potboiler of three interconnected romances, all taking place in the Midlands town of Middlemarch in the early 1830s. There’s Dorothea Brooke, the idealist who marries stuffy old academic Mr Casaubon but discovers she really loves the artist Will Ladislaw. There’s conceited Rosamond Vincy, who marries the brilliant young doctor Tertius Lydgate before finding cracks in his character that threaten to degrade her local standing. And there’s Fred Vincy, an idle, debt-ridden gambler who comes good and marries his childhood sweetheart Mary Garth. Between them there is a vast assortment of businessmen, rivals, servants, sisters and parents, all played by a multi-roling cast whose constant switches of character give the show a sense of rollicking momentum. In effect, it’s a long-running soap opera about everyday country folk. If it had been on Radio 4 they’d have had to call it The MiddlemArchers.

The outer world of cataclysmic change that characterised the 1830s – the Reform Bill, the railways, the abolition of slavery, the Factory Act – barely gets a look-in against the inward-looking lives of our unhistoric inhabitants. Which is of course the whole point.

And at the heart of the whole thing is the author, George Eliot, played by the winningly sympathetic Amanda Root. Eliot is on stage throughout. She is both narrator and confidante, interpreter and chorus. She explains the characters’ inner motivations. She gently prods them into action. They appeal to her for advice. She has one foot in their world and one in ours. Root is a joyful, warm-hearted companion, and she recreates the novel’s technique of the narrator commenting on her creations. But more than that, her presence makes the play not just about the good folk of Middlemarch, but about George Eliot herself. This woman who created a fake identity is herself a fiction, telling her own story refracted through the lives of Dorothea, Rosamond and co. It’s an ingenious theatrical device, although it keeps one foot very much in the original novel.

The RSC have played with authorial voices before. Their winter show from a few years ago, A Christmas Carol, had Charles Dickens arguing with his publisher about each scene as it played out. And back in 1980, their very first two-part Victorian novel adaptation, Nicholas Nickleby, featured the characters themselves acting as their own narrators (Roger Rees saying, ‘Who’s there? said Nicholas as he turned towards the door’). That approach was radical, confessional and intensely theatrical rather than literary. It felt like improv, like stage directions come to life. Middlemarch’s narrator stands at a more deliberate and thoughtful distance, a mother figure rather than an analyst.

So this version, directed by Jeremy Herrin with immense precision and sensitivity, is more a model of efficient, brilliant compression than an adaptation. Each scene is a little play in its own right, each character perfectly drawn. Nia Towle, as Dorothea, yearns for life even while it shrinks around her; Emma McDonald, as Rosamond, in a single, silent scowl at her husband’s hectoring, conveys all the tragedy of a life that missed its potential. Ian Drysdale, as the desiccated Mr Casaubon, wrings laughs from the audience merely by being so devoid of anything approaching humanity. John Hodgkinson, who last appeared here as a uniquely twisted Falstaff in Merry Wives of Windsor, once again leans deliciously into the villain role as Mr Bulstrode, the corrupt banker (and he counterbalances it quite superbly with a comic turn as a jocular auctioneer).

Every element of the production is finely judged and perfectly presented, from the gorgeous piano soundtrack performed live by Nathan Feeney, to Grace Smart’s design, featuring elegant chairs and tables that pop out of little trapdoors and unfold on cue. Above it all hangs an exquisite set of roof beams and arched braces, pegged and jointed with the sort of workmanship that came as standard in 1830 but sadly no more. It both protects and confines the characters – a symbol of the story itself.

In fact the only thing that disturbs the illusion is the repeated ringing of phones from the largely septua- and octogenarian audience. People talk of the problem of mobiles in theatres as if it’s an issue caused by young people being rude. This production proves the opposite. Ten phones going off over the course of the play is unacceptable. (To be fair, their owners aren’t trying to be disruptive: they just don’t know how to turn them off.)

But when they’re not groping for their iphones, the audience is involved in other ways. This Middlemarch, somewhat jarringly, has sections of audience participation. During the auction scene, characters sit alongside seats in the front rows and encourage the viewers to bid. In a local election scene, we’re urged to join in the chanting. Why? These little interludes don’t make us feel like we’re part of the action. Instead, they feel like the characters trying to reach out of the limitations of their own world, before returning to it.

And that is the touchstone of this production: trying, and failing, to break free from obscurity. When Amanda Root, as George Eliot, delivers her final line (lifted straight from the book) about the quiet but beneficial impact of unremarkable lives – ‘the growing good of the world is … half owing to the number who lived faithfully a hidden life, and rest in unvisited tombs’ – there are murmurs of emotional assent from the audience, who perhaps sense the proximity of those unvisited tombs more now than when they first read Middlemarch. They can’t escape. They can’t escape their town, their unfulfilled ambitions, their own author, or the stage on which they’re stuck. Middlemarch may not have the unchained brilliance of a theatrical reinvention, but it’s a fitting tribute to Mary Ann Evans.