Across her prolific 30-year career Emma Donoghue’s novels have ranged widely both in time (back as far as AD600) and place (from Ireland and the French Riviera to Canada and the west coast of the US), but perhaps the most striking feature of her work remains the devastating intensity she brings to bear on constrained, often profoundly claustrophobic spaces. From the scrap of an island in Haven to the maternity ward in The Pull of the Stars, from Anna’s cramped bedroom in The Wonder to the harrowing 11ft-by-11ft confinement of Jack and Ma in her multimillion bestseller Room, Donoghue is a master of the microcosm.

The rules and privations of a small girls’ boarding school in the early 19th century must have proved an irresistible lure. In Learned By Heart, Donoghue explores the real-life relationship between Anne Lister and Eliza Raine when the two girls were pupils at Miss Hargrave’s Manor school in York. Lister, best known to modern audiences as the inspiration for Sally Wainwright’s BBC drama Gentleman Jack, was a landowner, a businesswoman, a prolific diarist and openly lesbian; in 1834 she exchanged rings with Ann Walker at York’s Holy Trinity church in the first recorded lesbian marriage ceremony in British (and possibly world) history.

Much less is known about Eliza Raine, who was born in Madras, the illegitimate daughter of an English father and an Indian mother, sent back to England at the age of six and orphaned shortly after. In 1814 Eliza was committed to an asylum where she remained incarcerated for the rest of her life. Scholars have claimed her as the inspiration for Bertha in Charlotte Brontë’s Jane Eyre.

There is no doubt that the two girls were deeply involved. While the first known surviving entry of Lister’s diaries was written after she had already left the school, it was prompted by a long visit to the Listers by Eliza. The two girls continued to write passionately to each other for years, Eliza addressing Anne as her “darling husband”, until forced by Lister’s infidelities to accept that they would not have a future together. While Donoghue’s novel chooses as its focus the “less than a twelve month” that they spent at school together, the narrative is intercut with letters written 10 years later to Anne from Eliza in the asylum as she reflects, sometimes with anger and bitterness, more often with a terrible longing, on these golden schooldays when “the only lesson I learned, or at least the only lesson I remember, were you”.

In a piece in this newspaper in 2010 Donoghue named Anne Lister as her hero: in the acknowledgments to Learned By Heart she says Lister “changed my life”. But though her novel is written from the perspective of an increasingly besotted Eliza, it is no hagiography. Donoghue’s Anne is a mass of complexities and contradictions. Clever and perpetually curious, with a prodigious memory and a daredevil streak, she is also frequently insensitive, a ferocious showoff, and a howling snob. Most of all she is, for her time and class, jaw-droppingly outspoken, and it is her candor as much as her charisma that attracts Eliza who, prior to Anne’s arrival, has made it her business to remain as invisible as possible.

If she had confined herself to the tiny world of the Slope, Learned by Heart would have been a triumph. A trademark of Donoghue’s fiction is her blend of profundity and plot, but in this novel she has allowed research to take the place of action. The book brims with the minutiae of school life, the lessons studied and games played, the outings taken and the many draconian rules and regulations. While these are interesting enough, they do little to keep the pages turning. Just like Eliza, I found myself wishing away the long passages in the classroom or in conversation with their many classmates, impatient for the moment when Eliza and Anne could once again sneak up to the Slope and let the irresistible spark of their attraction reignite the story. This is Donoghue’s superpower, after all: to find the universal in the smallest of spaces. Besides that, the outside world – and the world of school in particular – is simply less compelling.