In August this year Agnes Chow crossed into mainland China filled with fear. The young activist was in the company of five national security police, taking her from her home in Hong Kong, on what she says was a “propaganda tour” organised by authorities in return for her being allowed to study overseas. Police had told her the tour was mandatory if she wanted them to return her passport, which they’d confiscated years earlier as part of her bail conditions. Chow is a key figure in Hong Kong’s most significant pro-democracy movement in the last decade, pushing back against Beijing’s...