Diana and Leo is the sequel to The Alchemist and the Silurist, a historical novel based on the sometimes tortured life of Thomas Vaughan, the 17th-century Welsh Anglican pastor, who became obsessed with alchemy, and his twin brother Henry, the mystical poet known as the Silurist. Stories of the controversial alchymist Thomas Vaughan were revived and embellished some two-hundred years after his death by a rougish French writer named Gabrielle Jogand-Pages who, under the pen name Leo Taxil, created elaborate hoaxes, pitting Freemasons against Catholics. Taxil published a series of salacious and ficticious accounts of the imagined activities of a young American girl named Diana Vaughan, who had journeyed to Paris hoping to prove her kinship to the 17th-century Welsh scientist. The novels were written by 83-year-old James E. Vaughan, a distant kinsman of the twins, after twenty years of careful and exhaustive research.