As his 50th birthday dawned, Peter Dunne set out to leave a trail of metaphorical breadcrumbs for his three children, so that if they ever needed to know what their father might have had to say they would have him to hand: from compromise to compassion, and democracy to sacrifice, Dunne explores the social mores and morality of our time and tries to answer the eternal questions that line the path to peace of mind. He talks to Sarah Crown.