The Conboys’ experiment gave a young Harvard medical school graduate a big idea. But, there is a big gap between the experiments they did with mice in the lab, and pumping young blood into human beings.

Still, he registered his company, Ambrosia Plasma, on the Food and Drug Administration clinical trials website and began an ambitious human research experiment. For $8,000 in cash, cheque or digital transfer, anyone over the age of 35 could receive two litres of blood plasma from 16-25 year olds in their veins. The outcomes were ambitious - physical rejuvenation, weight loss, reversal of dementia, and healthy looking skin.

Does this fairy tale have a happy ending?

In this series, technology reporter and psychologist Aleks Krotoski explores the frontiers of the extreme longevity pioneers. They've made their money in Silicon Valley. And with their technology solutions - PayPal, Facebook, cryptocurrencies - they've ushered in the world that we live in today, with all its unintended consequences. Some of them now want to solve the "problem" of aging, or even death, and they are making bigger strides than we may think.

Can they? Should they?

A Pillowfort production for BBC Radio 4

New episodes released Mondays. If you're in the UK, listen to the full series of Intrigue: The Immortals first on BBC Sounds: bbc.in/3WEQS5W