Memory is dangerous in a country that was built to function on national amnesia. A single act of public remembrance might expose the frailty of the state’s carefully constructed edifice of accepted history, scaffolded in place over a generation and kept aloft by a brittle structure of strict censorship, blatant falsehood and wilful forgetting. That’s why a five-foot-tall, 76-year-old grandmother poses enough of a threat that an escort of state security agents, at time as many as 40 strong, has trailed her to the vegetable market and the dentist.

Louisa Lim has released a book she didn’t want to write: The People’s Republic of Amnesia: Tiananmen Revisited. How did China systematically forget what happened June 4, 1989, in Tiananmen Square?