Dallas, 22 November 1963. The main event is supposed to be downtown, on Main Street. News footage shows office workers leaning out of windows, peering at the motorcade through a blizzard of ticker tape. On the sidewalks, the crowds are fifty deep, a wall of noise and celebration. Everyone thinks this is the place to be.

A few blocks away, in Dealey Plaza, the air is different. There is no ticker tape here. The crowds are thin. The only person filming is a dressmaker balanced on a concrete plinth. In this quiet corner, there's a man opening an umbrella even though it isn't raining, a construction worker in a hard hat who claims he was sent here by God, three tramps who stand on the verge of becoming suspects, an unidentified witness known only as the Babushka Lady, and many more.

This is not a book about conspiracies or a lone gunman. This is a book about memory, about how we construct our shared history, and about what happens when your life is defined by a single, fleeting moment. It's about a group of real people who opted out of the main event before John F. Kennedy was assassinated, only to find themselves accidental witnesses to the most scrutinised six seconds of the twentieth century.