It was an idle click on an unpromising website that first directed Nora Crook towards the most exciting and unexpected discovery of her distinguished academic career. Crook, a professor emerita at Anglia Ruskin University and expert on the Romantic period, was researching an obscure 19th-century novelist when her internet search brought up a listing for 13 documents at Essex Record Office, catalogued under the tantalising words: "Letter from Mary Wollstonecraft Shelley".

"I thought: 'What is this?' and clicked on the link," she said. "I knew right away they had never been published before."

Thanks to "pure serendipity", Crook had chanced upon the largest collection of unpublished letters by the author of Frankenstein to be discovered in decades....