Most of us will never have been to a Tupperware party, but we’ll still have an idea of what that phrase means: it’s a form of ‘multi-level marketing’ (MLM) in which top salesmen recruit ‘downlines’ of other salesmen, who recruit local agents to sell a product, whatever it may be, direct to consumers, who are often friends and neighbours. Commissions then flow back up the line, the top salesmen collecting a good living while lower ranks make pocket money. The concept was perfected in 1940s America as a way of selling Tupperware plastic containers. Around the world today, a hundred million people are involved in MLM businesses selling coffee, cosmetics, kitchenware and much else besides. It’s a legitimate form of enterprise so long as there are genuine products to be sold at the end of the line.

If there aren’t, it’s a ‘pyramid selling’ scam. If there’s nothing there at all but existing investors are paid rewards out of what new recruits have paid in (the modus operandi of the fraudulent New York investment manager Bernie Madoff), it’s called a ‘Ponzi scheme’. These long-established ways of ripping off the gullible are what the Bulgarian-born fugitive from justice Ruja Ignatova stands accused of practising, on a multibillion-dollar scale, through the invention of OneCoin, the cryptocurrency that never was.

This is a remarkable tale of the exploitation of what the 19th-century writer Charles Mackay called ‘the madness of crowds’. The Missing Cryptoqueen, which derives from a BBC podcast of the same name, follows Ignatova as she embarks – with a crew of MLM super-salesmen, dodgy lawyers, offshore financiers