In the backroom of an unassuming antiques shop in Hong Kong, Gino Caspari discovered treasure.
The Swiss archaeologist, who was posing as a buyer in order to investigate Hong Kong's black market,
knew about Sanxingdui masks: strange faces, heavy-lidded and thick-lipped,
buried in sacrificial pits in south-west China 3,500 years ago.
China's government had designated some as "grade-one national treasures", meaning they were subject to strict export controls.
So Mr Caspari was shocked when a dealer showed him
what appeared to be a Sanxingdui mask hidden in the back of his shop.
And this mask was exceptional: its eyes were filled in, unlike those on known pieces.
Study of it could therefore make a real contribution to archaeology.
(The eyes also suggested the mask was real: forgers tend to copy existing artefacts.)
What was it doing in a shop in Hong Kong?
Since 2012 China has recovered more than 2,300 pieces through auctions and diplomacy.
America alone has returned 600 smuggled cultural artefacts.
Rich Chinese also started buying up such rarities
as a way to demonstrate both prosperity and patriotism;
prices for Chinese antiquities rocketed as a result.
"Cultural relics and cultural heritage carry the genes and blood of the Chinese nation,"
So it is surprising that Hong Kong, which reverted to Chinese rule in 1997,
is "one of the main gateways for the illicit antiquity trade out of China",
says Steven Gallagher of the Chinese University of Hong Kong.