On October 7, 1816, Mary Godwin — she would not become Mary Shelley until she and Percy Bysshe Shelley married in December — was nineteen years old and living near Lake Geneva, where the summer's unusual weather had confined the household indoors and prompted the ghost story competition that produced Frankenstein. She was already pregnant with their second child. The first had died.

Mary Godwin was born in 1797, the daughter of the philosopher William Godwin and the feminist writer Mary Wollstonecraft, who died eleven days after her birth. She grew up in her father's intellectual household, read widely, and began a relationship with Percy Shelley when she was sixteen. She was with him at the Villa Diodati when Lord Byron proposed that each member of the company write a ghost story.

Frankenstein, or The Modern Prometheus was published in 1818 anonymously, with a preface by Percy Shelley. Reviewers assumed the author was Percy. The preface's authorship and the novel's authorship were conflated, and the attribution of the novel to Percy Shelley persisted in some quarters for years after Mary's identity as the author was known. Percy's preface was helpful; his promotional instincts were his own.

She wrote the novel at eighteen. It invented the science fiction genre. The themes — scientific creation without ethical accountability, the consequences of abandoning what you make — have not become less relevant.

Percy Shelley drowned in 1822. Mary Shelley spent the remainder of her life editing and publishing his work, writing five more novels, and raising their son. She is usually introduced as Percy Shelley's wife.