On 12 March 2020, the bitcoin cryptocurrency plunged by nearly 40% – the worst selloff in seven years – as the coronavirus pandemic swept the world.

One hedge funder described what traders called “Black Thursday” as a “bloodbath across the board”, with crypto falling harder and faster than the stock markets. Many individuals who, in effect, bet on the currency rising in value, saw those investments wiped out.

But one company, BitMEX, a crypto trading platform with offices in Hong Kong, emerged from the crash virtually unscathed. It was claimed it had turned a market crisis into a “profit centre”, with an estimated $12.3bn of trades in just one day.

A new legal action focusing on exactly what happened on 12 March that year…