On the eve of what would have been the world's largest share listing, Ant Financial founder Jack Ma, the Chinese billionaire mysteriously disappeared. Things started to go wrong for Ma after he told a room full of banking regulators that their methods were out of date and not fit for purpose. Shortly afterwards, the Chinese government cancelled the listing and Jack went silent. So what has happened to Jack Ma? Journalist Celia Hatton, who spent 15 years living and reporting in China, investigates.