When, at the beginning of 2008, Antoine Castel took control of the fixed-income unit in Beijing of Calyon, the investment banking arm of Crédit Agricole, the world's biggest banks were making fat profits in China's nascent derivatives markets.
But just weeks into his new job at the French bank, Mr Castel watched in horror as Chinese companies began to lose billions of dollars on the bespoke trades they had struck with western dealers. It was the start of a chain reaction that this summer unleashed a fierce backlash from regulators and local banks.
In stark contrast to the slow pace of reform in derivatives markets in the US and Europe, China's regulators have in recent months shut down the main route by which foreign banks sold derivatives from offshore operations and have banished speculative deals – moves that have important implications not only for Chinese companies and foreign banks, but also for the evolution of China's capital markets and the internationalisation of the renminbi.