Couples can't always make a baby with ease, and for the one in six couples who struggle to do so, there's another significant minority who may never conceive at all - even with the patchy NHS or repeated, and eye-wateringly expensive help that our evolving science of reproduction has to offer. In her first book, The Pursuit of Motherhood, Jessica Hepburn shared her heartbreaking journey through 11 rounds of IVF, miscarriages and an ectopic pregnancy, leaving us hopeful that she could still strike gold. In 21 Miles she follows up her intimate story with yet another way she mines her indefatigable spirit of endurance to beat the odds: swimming the 21 miles of the English Channel, while she ponders the meaning of the motherhood that she spent the previous decade pursuing.

Jessica's gruelling training schedule involved one relatively small pleasure: eating, a lot. With this in mind, she invited 21 women who have inspired her to share food with her, while she talked with them about their varying ways of making sense of life with or without motherhood - as well as requesting from each invitee the gift of a single word to buoy her across the sea. We meet women who haven't had children: Susan Greenfield, a professor of neuroscience and Camila Batmanghelidjh, the ex-head of the sadly disgraced Kid's Company, as well as the Labour MP Fiona Mactaggart. We also meet the polar explorer Ann Daniels who left her triplets at home in infancy to reach 90 degrees north, and the restauranter Prue Leith who adopted a daughter after having a biological child, and the record-breaking for the slowest crossing Channel swimmer, Jackie Cobell who has fostered children for over two decades.

Jessica's chosen women, unsurprisingly, come to their own view of how they make sense - or not - of their roles in the world. Kim Longinotto, the documentary film maker devoted to challenging female oppression, and a mother, stands out for me, '...it's this idea of your own biological child: that it's yours and it belongs to you. It's the root of a lot of evils in the world; it's what led to female genital mutilation and chastity belts and this obsession with women being pure. Because the link to that is that the men need to know that the child is theirs.'

It's worth finding out what Jessica's own conclusions are: to the puzzle of her own once all-consuming quest to have her own biological child, but also if she will eventually make it onto French sand. Like IVF, the odds of a successful Channel swim are heavily against you. Jessica wins over the reader with her sparkling style, yet her self-deprecating humour also belies an undertow of tremendous sadness too: of an enormous grief of an invisible loss that our society has yet to appreciate, and, also, of her partnership unravelling as she swims on, and on, and on. I laughed, and I cried, in equal measure. Mothers, and non-mothers should find resonances throughout - as I hope fathers, and non-fathers may too.