For Jane Austen, ‘abroad’ was Lyme Regis. What if the author, celebrated on postage stamp and banknote, had ‘seen the world’? Women writers in the early 19th century rarely needed their passports. A notable exception was Mary Shelley. Compare the description of the Alps in Frankenstein (conceived under their looming shadow) to that in Ann Radcliffe’s The Mysteries of Udolpho, woven out of superheated fantasy and Salvator Rosa’s pictures.

For Anne Brontë, ‘abroad’ was Scarborough, whose sands she glorified in Agnes Grey (she had herself buried overlooking the town). Emily Brontë experienced a foreign country, Belgium, only briefly and left as soon as she was able to. Her one surviving novel is microscopically local, venturing no further afield than Penistone Crags. There is only one Brontë sister who can be called ‘travelled’, something that, the proverb assures us, broadens the mind.

Helen MacEwan argues that British readers do not appreciate how deeply Charlotte Brontë and her fiction were steeped in her experience of spending two years in Brussels, and how this brought about that proverbial broadening – a dimension lacking in her novel-writing sisters. The complex hero of her novel Shirley, Robert Gérard Moore, is half Yorkshireman and half Belgian. Seen through her fiction, Brontë is similarly hybrid.

In the early 1840s, Emily and Charlotte intended to set up a school (and avoid the penal servitude of governessing). Their reason for going to Brussels in 1842 was to learn the ropes in a girls’ boarding establishment, the Pensionnat Heger-Parent. Emily stayed there for a year. While teaching at a Yorkshire school she had once claimed to prefer the house dog to her pupils. Charlotte spent two years there and would have stayed longer had not her passion for the school’s married, uncomplaisant proprietor, Constantin Heger, made it impossible.

The sisters chose Brussels because it was cheap. The city then was not today’s European mega-hub. Belgium itself had only been Belgium since the ‘revolution’ of 1830, which broke it off jaggedly from the Netherlands. The capital’s population was, during Charlotte’s stay, 113,000 – smaller than that of Bradford, the British city she knew best. It was, said Baudelaire, a petite ville. Charlotte called it Villette (puny town), the name serving as the title of the greater of her two novels set in Brussels. In the same work, the country of Belgium she named condescendingly Labassecour – the farmyard.

Such insults still hurt. There is no Brussels street named after the Brontës or memorial plaque other than a terse notification erected by the British Brontë Society over the site where the Pensionnat Heger-Parent once stood. It was and is still more vexing to Bruxellois, then and now, that Villette and The Professor (Brontë’s first Brussels novel) did not sufficiently showcase the grand Brabant monuments of the city. Charlotte dulls Brussels grandeur.

Charlotte was not alone. Other great writers of the century who found themselves for any length of time in Brussels liked to look down their noses at the city. Gérard de Nerval, regarding the Senne – the piddle running through the centre of Brussels – asked, recalling nostalgically the homophonic Seine, ‘What kind of capital is a city where you can’t even drown yourself?’ In fact the Senne, which served as the high town’s sewer, killed very efficiently, reducing by disease life expectancy in the lower town to eighteen years (Haworth, home of the Brontës, could proudly boast an average life expectancy of twenty-five years).

Baudelaire, driven to refuge in Brussels by scandal and debt, thought it worse than prison. ‘Only the dogs are alive,’ he grumped. Charlotte concurred. The Belgian character was ‘singularly cold, selfish, animal and inferior’ (‘animal’ is an odd word) and Belgians’ principles were ‘rotten to the core’. Marsh phlegm, not quick French blood, ran sluggishly in their veins. The one thing the Bruxellois were good at, she and others granted, was espionage. They hinged mirrors on their window casements so they could peek at the world outside. There was, as Villette attests, a lot of spying at the Pensionnat Heger-Parent.

Charlotte wrote The Professor while still throbbing with the experience of travel and hopeless love. It was not published in her lifetime but caught the eye of her publisher, George Smith, who promptly commissioned Jane Eyre. Charlotte, as a somewhat far-fetched legend has it, left Brussels with the promise je me vengerai. If so she served up her vengeance, as Don Corleone prescribes, cold, waiting nearly ten years before writing Villette.

MacEwan, a learned Brussels resident, levels her points coolly and authoritatively, assisted by rich illustration. What, then, was the ‘broadening’ that fed Charlotte’s oeuvre? It is evident most clearly in Villette, the sole work by Charlotte that can be called autofiction. Boundaries, the novel testifies, were broken in Brussels, releasing a genius more transgressively creative than that of Charlotte’s sisters.

The fiercely Protestant author, like her heroine Lucy Snowe (originally Frost), melted towards Catholicism, taking confession in the church (now cathedral) of St Gudula. An astonishing surrender. Both author and heroine of Villette fell in love with their professeurs. In Charlotte’s case, she did not, apparently, try hard to suppress adulterous desire. An even more astonishing surrender.

Such behaviour presages Jane Eyre hearing Rochester’s ethereal summons and racing back to him – still a married man, she believes. She will defy the seventh commandment nonetheless. Luckily Rochester has defied the sixth, murdering the luckless Bertha (as one can plausibly suppose). What would Charlotte have done had Heger, mad with love, summoned her?

It’s a fanciful supposition, but sufficient to suggest that Helen MacEwan has done what she set out to do. She gives us a complicatedly creative, if invincibly troubled, Charlotte to read with eyes opened wider. MacEwan’s work should find a place on every Brontëan’s bookshelf.