When protests swept Hong Kong last year, Alexandra Wong, better known as ¡°Grandma Wong,¡± always seemed to be there. Day after day, she stood out among the hundreds of thousands of demonstrators as a small woman with short gray hair waving a large British flag.

Then, during a few tumultuous days in August when the police fired tear gas in a subway station and protesters shut down the city¡¯s airport, Wong, 64, suddenly vanished.

Her friends in the movement quickly had their suspicions. They believed she had disappeared into China¡¯s opaque legal system, an alarming outcome for protesters that has become all the more chilling after Beijing imposed a national security law on Hong Kong this year. When Wong finally reemerged last month, she confirmed that she had been detained by the Chinese authorities.