A beautiful, unforgettable story of how a little boy's life was saved by a heart transplant - and the sacrifice that required it In 2017, Dr. Rachel Clarke read a newspaper article about a boy named Max who was slowly dying in a children's hospital. Nine months earlier, Max had been a typically ebullient nine-year-old, obsessed with soccer and music. Then, from nowhere, a virus ravaged his heart, causing it to fail. Max had not left hospital since. Without a transplant, he was doomed. But pediatric hearts are in desperately short supply, and Max seemed destined to become one of the one in five children who die while waiting on the transplant list. His parents were painfully aware that the only thing that could save his life was the death of someone else's child - the brutal arithmetic of transplant surgery.

On 31 July 2017, eight-year-old Keira Ball suffered a catastrophic brain injury when the car her mother was driving careered into oncoming traffic. When Keira was declared brain dead two days later, and even though his wife and son were also critically ill in the same hospital, Keira's father didn't hesitate to offer her organs for donation. Her heart, lungs, liver and kidneys saved the lives of two adults and two children, one of whom was Max. Organ transplantation is both a marvel of modern medicine and one of the purest expressions of human altruism. Recipients of donor organs are now planning their child's birthday party, setting off on a bike ride, enjoying an ice cream, or savouring the summer sunshine, thanks to the gift of another person's heart, liver, kidney or lungs. Without this radical kindness, the vast majority of these individuals would be dead. And none of them would be alive without the doggedness, toil and creative genius of doctors and scientists whose obsession and brilliance led to the 20th century medical breakthroughs that enabled the death-defying act of removing an organ from one human body and successfully reimplanting it in another. Rachel Clarke describes how Max's family welcomed Keira's parents and siblings into their home to meet the boy whose life she had saved.

With trembling fingers, Keira's mother placed a stethoscope on Max's chest. Through his T-shirt and the thick ridge of scar snaking its way across the length his chest, she heard the beat - indefatigable, incomprehensible - of her daughter's heart as it pumped life through Max's body.