Katherine de Mattos and Robert Louis Stevenson were cousins, and very fond of each other. Their friendship was deep. For those who believed RLS to be alone in the South of France prior to writing Travels with a Donkey, he was not. Nothing scandalous going on, but her presence had to be kept secret. Otherwise RLS might has found himself unjustly named co-respondent in her divorce. She was fleeing a bad marriage, and he was providing emotional and material support. She was also a seminal influence on his literary career, penning the short story The Red-Litten Windows. Whether she wrote it before Dr Jekyll and Mister Hyde, or contemporaneously is not certain. That the pair discussed the idea of duality at length is undisputed, and that she, thereby, influenced his novel was acknowledged by him dedicating it to her.

And yet, later, because of another story, things turned so sour that he cut her off completely. This is a story of plagiarism; of Stevenson’s wife, Fanny, stealing an unpublished story from her friend, rewriting, polishing and publishing it under her own name with no acknowledgement. De Mattos didn’t even call her out on it, but De Mattos’s agent, William Henley, the inspiration for Long John Silver, did. And things got very messy. Friendships were broken, grudges held for lifetimes, and Katherine de Mattos, who remained in love with her cousin all her days, suffered the most. But at least she did not issue a public apology for something she had not done, which her cousin was demanding.

There’s a piece of Hyde in all of us. RLS was no exception.

This is the shocking incident at the centre of Hodge’s book, but there is a much broader focus: the story of Stevenson’s and de Mattos’s childhood, the influences and development of his career, her bad marriage, his meeting of Fanny and her acceptance of losing him to a rival, the undoubted advantage that Fanny had with RLS as first reader (and editor), and the difficulties De Mattos had getting published. He includes two De Mattos’s stories: the aforementioned Red-Litten Windows and The River House – which lays bare De Mattos’s grief at the ruined relationship. There is also a piece written for The Magazine of Art (which is how she supported herself and her two children after her divorce). Writings of greater historical than literary interest, I would argue. (There’s a reason why she struggled to get published.) Fanny Stevenson’s The Nixie – the stolen story – is also included. It makes much better reading, but oh, those dubious ethics!

Ghosting isn’t new to the 21st century, but what a way to treat your loyal childhood friend, possible first love, and the woman, who, alongside your wife, helped save your life during a particularly severe TB haemorrhage.

Cousin Hyde indeed.

What a fascinating book. Perfect reading during last week’s sojourn in the Scottish capital.