Had Onan not spilled his seed upon the ground, he might have invented invisible ink. The possibility had not occurred to me until I read this account of the start of Britain’s intelligence services. Even then the implications seemed so startling as to be barely credible — that the entire trade in espionage, including the serried ranks of Cheltenham’s GCHQ, the massed battalions at Fort Meade’s National Security Agency, the MI5s, 6s and other shadowy digits, not to mention literature’s denizens, from Ashenden and Greenmantle to James Bond and George Smiley, owed its origin to solitary sex.