What would it be like to be swallowed by a whale? Disappearing into the huge maw of a sea giant has made for thrilling and terrifying narratives, from the biblical story of Jonah to Melville’s Moby-Dick and Walt Disney’s Pinocchio. But here’s a stranger idea: what if you were already living inside a whale but didn’t realise it, so vast were its cavernous insides? For an idea this odd and haunting, you would have to look to the works of John Donne and, more specifically, to what is by far his most bizarre poem, ‘Metempsychosis’, which tells the story of the migration of a single soul from entity to entity, from the apple picked by Eve in Eden through a head-spinning range of animal and human creatures. It’s as part of this hallucinogenic bestiary that we encounter the whale, with its pillar-sized ribs and ‘thunder-proof’ hide, and are told that ‘Swim in him swallowed dolphins, without fear,/And feel no sides, as if his vast womb were/Some inland sea.’

I’ve always been haunted by these lines – by the question of how to interpret them and whether they should be interpreted at all. Are the dolphins somehow a metaphor for our condition as humans, believing that we are free so long as we remain oblivious to the restrictions within which we operate? Does Donne call the whale’s abdominal cavity its ‘womb’ innocently – the word could just mean ‘stomach’ in this period – or is there a deliberately gender-bending quality to this whale teeming internally with life, making it a symbol of pregnancy? Or are the dolphins just innocent sea creatures, brought idly to life by a poet allowing his imagination to go on a surreal holiday in a poem so strange that one critic in the 19th century called it ‘the effusion of a man very drunk or very mad’?

The agility of Donne’s imagination and the sheer pyrotechnic weirdness of his writings have made him both irresistibly attractive to biographers – who wouldn’t want to understand the man behind poems like this? – and particularly elusive of biographical scrutiny: what set of facts could possibly help to explain such a person? Katherine Rundell’s excellent Super-Infinite approaches Donne with keen and frank awareness of these temptations and the pitfalls they conceal. She recognises the double bind in which Donne’s works place his readers: they are conspicuously difficult and erudite, demanding depth of knowledge, intensity of attention and speed of thought from those who would follow them, but bringing knowledge to bear upon their quicksilver shifts and spurts of imagination can feel like ramming a pin through the body of a particularly beautiful butterfly in order to taxonomise it. Rundell is scrupulously polite about R C Bald’s ‘spectacularly detailed’ life of Donne, the standard scholarly biography, calling it ‘the bedrock of this book’ in a footnote, but there has surely never been a duller life of a more exciting poet. Knowledge may be necessary, but it can be like an anvil dropped on the head of a mischievous cartoon character, stunning it briefly into passive silence.

Rundell’s response to this risk is to put herself and her reactions to Donne’s work into Super-Infinite, part of a recent tendency among writers, including Rachel Eisendrath (on Philip Sidney) and Anahid Nersessian (on John Keats), to bring canonical authors down from the glassy firmament into a more personal, earthly realm. She states near the outset that her intention is ‘both to tell the story of [Donne’s] life, and to point to the places in his work where his words are at their most singular: where his words can be, for a modern reader, galvanic … This is both a biography of Donne and an act of evangelism.’ The form that this evangelising takes is subtle, however. After a prismatic introduction that gives us snapshots of Donne some years apart, introducing us to the markedly different guises in which he will appear, the book settles into a predominantly chronological narrative, sliced into brief and bite-sized portions. These follow Donne, born in 1572 into a Roman Catholic family haunted and decimated by persecution, from his childhood, through his younger years spent as an adventurer in the Earl of Essex’s expeditions to Spain and around Lincoln’s Inn, where he became renowned as a writer of daringly contorted and riveting poetry, and then on to the first turning point of his life, his outrageous clandestine marriage to a teenage girl named Anne, which saw him imprisoned and then forced for some years to wander aimlessly in the professional wilderness until he eventually took holy orders and became dean of St Paul’s. By the end of his life, he had established himself as the most famous and admired preacher of the age, kings and crowds straining to unpick every sentence of his sermons as they unfurled.

Rundell tells these stories engagingly, striking a good balance between the thorough and the necessarily brisk. This book’s most obvious predecessor in the mixing of information, interpretation and opinion is John Carey’s classic study John Donne: Life, Mind and Art (also published by Faber, four decades ago), though Rundell leans more than Carey towards biographical linearity, and is less inclined to see Donne’s religious conversions as the key to his tangled mind.

While this biographical narrative is perfectly well executed, it is not where the book comes to life. What truly matters, and makes Super-Infinite emphatically worth reading, is that Rundell is a writer. Her evangelical urges are expressed not in explicit exhortations to read Donne, but via the forms of responsive expression that he has inspired in – wrung from – her. Rather than telling us why Donne is worth reading and absorbing into one’s way of thinking, her writing shows us. Everyone knows that Donne is witty; Rundell wonderfully tells us that ‘he wanted to wear his wit like a knife in his shoe; he wanted it to flash out at unexpected moments’. She can brilliantly capture the elusive posture of knowing ennui that Donne often adopts, ‘caught somewhere between the suggestive eyebrow and the yawn’. She selects sequences of adjectives that ask the reader’s mind to move quickly in unexpected directions, like Donne’s own notoriously far-fetched metaphors: Donne wanted death ‘to be explosive, multicoloured, transmogrifying’. She calls the deanship of St Paul’s, a staid vocation if ever there was one, ‘a fantastic piñata of a job: hit it, and perks and favours and new connections came pouring out’. Without ever claiming to think like Donne, she shows in every paragraph how Donne has enabled her to think.

Rundell is best known as an author of books for young people, and those who have read those books, as I have, to their children will know that she is particularly adept at capturing childhood as a condition of movement – of dynamism and fluidity not yet co-opted by the systems of the adult world. I didn’t know before reading Super-Infinite that she had a background as a scholar of John Donne’s work, but I did know from reading interviews with her that she had spent some of her time as a student in Oxford climbing by night across the rooftops of colleges, a pastime that she bequeaths to the young protagonists of books like Rooftoppers and The Good Thieves, miniature daredevils pirouetting across the darkened skylines of Paris and New York. It makes perfect sense, however, that an author with a taste for this activity – which combines daring, virtuosity and a predilection for secrecy and for genuine peril – should be drawn to Donne, whose writing features these very qualities in abundance.