But there is a breathless, of-the-moment quality to In Search of Mary Shelley that undermines the consecration of author and work which the biography asserts as its venture. Sampson wraps her evidently wide reading and archival research in a jolly, gossipy, intimate tone, and opens chapters with establishing shots that look and sound like storyboarding for a BBC documentary. ‘I want to rewind the film,’ she writes, ‘to bring Mary closer to us, and closer again, until she’s hugely enlarged in close-up. I want to see the actual texture of her existence, caught in freeze-frame. I want to ask what we do in fact know about who and how and why she is – who she is – and about how it is for her.’

Beneath its cinematic inflations, such a desire is sound and potentially fascinating. This is the first biography of Shelley to appear this century, and it comes at the end of generations of masculine misprision and gendered diminishment of Mary’s achievements. Sampson convincingly shifts the weighting of literary reputation from Percy Shelley, Lord Byron, and Mary’s father, William Godwin – and who, aside from determined antiquarians, reads much of these men outside the life-support wards of the academy these days? – to Mary Wollstonecraft, author of the A Vindication of the Rights of Women (1792), and her daughter and namesake, who, in the figures of Victor Frankenstein and his monstrous creation, managed to capture the psychological texture and technological implications of an emergent modern age.

The most potent argument this biography mounts is that Mary Shelley’s insights in Frankenstein could only have emerged from female experience. The story Sampson tells is reverse-engineered, so that Mary’s life is explored in order to illuminate the impulses, drives, attitudes, fears, and terrors which make Frankenstein so durable and intense, even today. The biographer concentrates her attention on the effects of her young subject growing up as a para-orphan (Mary Wollstonecraft died of puerperal fever after giving birth to Shelley; she was displaced by step-siblings and a strong-willed stepmother, and exiled from her family for long periods during her teens). Sampson wonders at Mary’s early experiences of psoriasis or eczema: episodes that would leave the girl in agony, whole limbs wrapped in poultices and bandaged up.

Sampson also lingers over Mary’s experience of childbirth and childrearing. In that era, she reminds us, babies were still called ‘animals’, and she manages to capture something of the uncanniness that clings to children, who are both of us – rhyming in personality and appearance – and yet irrevocably other. Though the biographer is alert to the scientific flavour of the day, with its experiments with electricity and galvanism, and while she is careful to give due weight to the philosophic and aesthetic currents that flowed into the mighty river of imagination which is Frankenstein, the ambivalence that attends motherhood and the fleshly reality of childbirth belong to Mary alone. It is her embodiment as a woman which provides the crackle and blast that runs through the muscles of her most memorable narrative.

Inevitably, this concentration on the first two decades of Mary Shelley’s life (she was eighteen when the idea of the book was born out of that infamous booze-and-laudanum-fuelled night spent in the Villa Diodati on the shores of Lake Geneva with Shelley, Byron, and John Polidori, future author of The Vampyre, and in her early twenties when the book was anonymously published to immediate and near-universal acclaim) means a degree of telescoping: the remainder of her work and life following the publication of Frankenstein takes up less than a hundred pages.

Portrait of Mary Shelley by Richard Rothwell, 1840 (Wikimedia Commons)The result, then, is something less than a biography and more than an extended gloss on a work of fiction. Sampson has laboured over primary documents and obviously read widely around her subject and those in the circles in which she moved, but the relative brevity of the exercise necessarily entails losses in sophistication and depth in arraying the fullest picture of Mary Shelley’s moment. William Godwin and Percy Shelley perhaps suffer most from this approach. Shelley, Sampson assures us, was a man of principle and true idealism. But her bullet-point approach to his actions in relation to Mary over time render him a creep, a cad, and what P.G. Wodehouse would call a ‘sinister vegetarian’ type.

Think of the alternate picture painted by Richard Holmes in his magisterial biography of Shelley, The Pursuit (1971). He is no less appalled by the actions of the male poets around Mary Shelley, but his willingness to dive into the poems of Percy and Lord Byron as a critic and historian of ideas gives real heft to any exonerative claims. The best of Percy Bysshe Shelley went into his work. Beyond that, Holmes manages to provide more empathetic attention to Mary in passing in his life than Sampson does with the subject at the heart of hers.

But comparisons such as this are unkind. Holmes’s immense undertaking remains one of the most remarkable achievements of the golden age of British biography. It will live for as long as readers retain an interest in the Romantics. What Fiona Sampson has done in this warm, timely, admiring biography is to keep that flame of interest alive. Sampson is convincing in her arguments about the feminine and the monstrous; she is unassailable in making the case that women are more likely to meditate on and worry about the proper stewardship of those whom they have bought into being.

Frankenstein was not a book that Percy Shelley or Byron could have conceived, because their biological nature did not permit them to. And even if they had the emotional imagination to overcome this lack, it was too easy for them to keep running down the tracks laid down by society for the benefit of their gender. Their radicalism was charismatic yet circumscribed. It was Mary Shelley who jumped the rails. Two centuries later, it is her new path – and that of her scientist and his monster – that the rest of us are still following on.