On a mild winter's evening in 1850, Isabella Robinson set out for a party. Her carriage bumped across the wide cobbled streets of Edinburgh's Georgian New Town and drew up at 8 Royal Circus, a grand sandstone terrace lit by gas lamps.

The guests were gathered in the high, airy drawing rooms on the first floor, the ladies in glinting silk and satin pulled tight over boned corsets; the gentlemen in tailcoats, waistcoats and neckties. When Mrs Robinson joined the throng she was at once enchanted by a Mr Edward Lane, a handsome medical student ten years her junior. He was 'fascinating', she told her diary, before chastising herself for being so susceptible to a man's charms. But a wish had taken hold of her, which she was to find hard to shake...