I once spent an evening, back in the mid-1980s, with William Colby, the legendary spy and director of the CIA. I was an undergraduate at the time, and the CIA’s Iran–Contra debacle was in the news. Lured by the agency’s mystique, I was eager to ask him about the fabled Phoenix programme he directed — a top secret initiative to target and eliminate Viet Cong who had infiltrated South Vietnamese villages, often conducted by Americans who had crossed over some invisible line, leaving behind them the normal life that comprised my world.