Angela Gui always heard from her father on her birthday, even as he was busy running a booming book publishing business in Hong Kong.
But when she turned 22 last week, there was only silence.
Her father, Gui Minhai, a naturalized Swedish citizen, had been missing for more than four months, along with his four business associates in Hong Kong. They had found a successful niche publishing books about political intrigue among China's Communist Party leaders; now they are in the custody of mainland Chinese authorities, apparently charged with selling illicit books.
In mid-January, Gui gave a morose confession on Chinese state-run TV, saying he had fled China while on...