Nicosia, Cyprus, 2018. Kiri Sofocleous sits down to write a Facebook message to a man she has never met. It has been 40 years since Kiri saw her childhood best friend but she has never forgotten her. Could this be the key to reuniting? Matthew Syed tells the story of one woman’s determination to find a beloved friend, lost for four decades due to a move abroad, a political divide and a mislaid address. It prompts him to explore why we make friends and how they influence the rest of our lives, even after losing touch. Professor Catherine Bagwell of Oxford College - Emory University, reveals how playground squabbles equip us with life skills and how making friends can be good for our mental health. Professor Robin Dunbar explains that we are looking for matches from a pre-programmed personal checklist. Building on Dunbar’s Number, the theory that each of us has 150 meaningful relationships, the Emeritus Professor of Evolutionary Psychology at Oxford University, sorts our connections into circles of friendship. Through Professor William Rawlins, Matthew learns how the friends of our young adulthood help us become ourselves, but ultimately write themselves out of our life story by encouraging us to follow our dreams. Contributors include firm friends Kiri Sofocleous and Sonya Foxsmith, Professor Catherine Bagwell of Oxford College - Emory University, Professor William Rawlins of Ohio University and Robin Dunbar, Emeritus Professor of Evolutionary Psychology at Oxford University. Presenter: Matthew Syed Producer: Marilyn Rust Executive Producer: Claire Crofton Researcher: Nadia Mehdi Series Editor: Katherine Godfrey Music, Sound Design and Mix: Nicholas Alexander. Theme Music: Seventy Times Seven by Iona Selaru A Novel production for BBC Radio 4