Hedge funds take great pains to hide their inner workings. So a recent court case in which Jane Street sued two former employees and Millennium Management, another fund to which they had jumped ship, was immensely pleasing to the firm’s rivals, since it offered a rare view into one of the industry’s giants. Among the revelations: Jane Street’s “most profitable strategy” did not play out on Wall Street, but in the unglamorous Indian options business, where the firm last year earned $1bn.