In June 2016, Dr Ruja Ignatova told an audience of thousands at Wembley Arena that her new cryptocurrency, OneCoin, was a "Bitcoin killer" and would make early investors rich. Many in the crowd had already poured in their life savings. Many more followed.
About £2bn from across the world was spent on OneCoin tokens, including tens of millions of pounds from British families.
Then, in late 2017, Ruja disappeared and the scheme was exposed to be a scam. There was no cryptocurrency. It was an old-fashioned Ponzi scheme.
For 18 months, I've investigated the scandal for BBC Sounds, for the podcast The Missing Cryptoqueen, alongside my producer, Georgia Catt.
After a break, we returned for a new episode last week, which focused in part on the UK's Financial Conduct Authority.
Just three and a bit months after the London extravaganza, the watchdog posted an online warning about the get-rich scheme, headlined: "Beware trading virtual currencies with OneCoin".
It said consumers should be "wary of dealing with OneCoin" and the organisation was being investigated by the City of London Police.
"This firm is not authorised by us and we do not believe it is undertaking any activities that require our authorisation. However, we are concerned about the potential risks this firm poses to UK consumers," it added.
This helped counteract the claims of OneCoin promoters, who were trying to pull in more victims.
And delighted critics would spend their evenings sending the FCA warning to potential new recruits.
But on or around 1 August 2017, with the scam in full momentum, the authority suddenly removed its notice.
Now, it was Ruja's turn to be thrilled.
According to retired libel lawyer David Hooper, it should have been obvious to the regulator OneCoin's promoters were going to use this "as a marketing opportunity".
And OneCoin promoters quickly began claiming it meant the FCA no longer considered OneCoin a risk.
One triumphantly told his followers: "If [the FCA] still thought we were a fraudulent company… then, guess what, that warning's not removed."
While making the podcast, we've seen letters a UK law firm hired by Ruja sent to her critics.
The letters threatened legal action unless they deleted online posts claiming OneCoin was a pyramid scheme run by a criminal organisation.
And at some point, one of Ruja's advisors - although it's still not clear exactly who or when - realised the FCA might have overstepped its regulatory authority.
And, according to multiple sources, the law firm pressured the FCA to have the notice removed.
All regulators have their own turf to referee.
The FCA's covers financial products and services.
What's included isn't always clear, especially with new products.
And being so novel, cryptocurrencies were, and still are, outside this "perimeter".
In response to a query at the time of its removal, the FCA said it "had been on our website for a sufficient amount of time to make investors aware of our concerns".
However, several alerts have remained live on the FCA's website for years, even decades. Not to mention the scam was still being heavily promoted in the UK at the time.
When we asked again, it told us the initial decision to publish the notice had been at City of London Police's request and the decision to take it down had been made "in conjunction" with the force.
"It did not appear that OneCoin was carrying on any activities that required FCA authorisation," it said.
"The FCA does not regulate crypto-assets and therefore it could not take this matter further.
"Any queries should be directed to the City of London Police on this."
We followed this up with the police force. But it made clear responsibility for the notice was the regulator's alone.
"The City of London Police was made aware of the FCA's intention to take down their alert on OneCoin and their reasons for doing so," said a spokesman.
"The force accepted that the decision belonged to the FCA given that this was their alert."
We went back to the FCA to ask again what its reasons were but it declined to comment further.
City of London Police ultimately dropped its own investigation, citing "insufficient evidence to support criminal proceedings" but was thanked by US prosecutors for helping them convict a lawyer who had helped launder $400m (£300m) of OneCoin's proceeds.
However, neither of these events happened until two years later, in 2019.
And critics believe once the decision had been made to issue the original warning, there was an obligation for the FCA and police to stick with it.
"They clearly had responsibilities not to pour a bucket of whitewash over OneCoin," Mr Hooper told us.
The hunt for Ruja continues - if caught, she faces up to 80 years in a US jail.
For the many thousands conned out of their savings, justice won't be served until the matter is revolved.
But in the meantime, many can't help feeling the UK authorities could have done more to thwart the scam and at the very least shouldn't have backtracked from keeping their concerns public.
Additional reporting by Leo Kelion