Was President Viktor Yushchenko of Ukraine poisoned on the orders of a Russian "political technologist" working for the Kremlin?
Mr Yushchenko says poison caused a sudden change in his appearance
That is one of the sensational claims being examined by Ukraine's chief prosecutor as he gets to grips with the new inquiry into how Mr Yushchenko - the main opposition candidate in last year's elections - apparently ingested a large dose of dioxin. It severely disfigured his face, and according to some accounts, almost killed him.
The allegation is contained in a leaked tape that has been impounded by the prosecutor. A copy has also been obtained by Newsnight, which has conducted its own investigation into the poisoning.
On Tuesday, the man at the centre of the allegation - Gleb Pavlovsky, the head of a pro-Kremlin Moscow think-tank, categorically denied the suggestion that he had thought up the idea of giving Mr Yushchenko the "mark of the beast".
"For what reason anyone would do this is hard to imagine," he told Newsnight. "And how I could have come up with the idea... it's absurd, and absurd that in Kiev it's being discussed seriously."
When the tape of an apparently tapped telephone conversation mentioning Pavlovsky was first aired on Kiev's Channel 5 television, it was widely dismissed as a falsification.
It was seen as a deliberate attempt by Pavlovsky's enemies in the Kremlin to discredit him after his failed attempts to promote the Kremlin's preferred candidate, Viktor Yanukovych, in the election battle.
The prosecution's decision to use it as evidence in their inquiry has surprised everyone - including Pavlovsky.
"When the tapes appeared on Channel Five, I took it as a joke," he told Newsnight. "A bit vulgar for my taste... in the style of Orson Welles... But when I heard the prosecutor-general had taken them, that turns a TV joke into a lie."
The criminal investigation is still in its fairly early stages. But the signs are that the possibility of a Russian link is one of its main lines of inquiry.
Mr Pavlovsky vehemently denies any involvement in an alleged attempt to poison Mr Yushchenko
Officials have said the poison could only have been produced in one of four or five laboratories, probably in Russia or the United States.
The interior minister claims he knows who brought the poison across the border, and which member of parliament accompanied it.
Viktor Yushchenko, who campaigned for more democracy and closer links with the West, was taken seriously ill on 6 or 7 September with severe abdominal and back pain.
He was flown to Vienna for emergency treatment. Doctors could find no explanation for his illness, but when he returned to Kiev he claimed he had been poisoned by the "political cuisine" of the Ukrainian government.
Suspicion centred on a mysterious dinner attended by Yushchenko on 5 September 2004 - hosted by Volodymyr Satsiuk, the deputy head of Ukraine's secret service, the SBU.
Mr Satsiuk has denied any possibility of poisoning at the meal - and Newsnight has seen a photo of him embracing Mr Yushchenko at the end of the evening.
The meeting was held under highly unusual circumstances. Yushchenko gave the order to dismiss his usual security detail. But he was apparently worried about attending. And his wife claims that when he returned there was an unusual metallic taste on his lips.
Volodymyr Satsiuk hosted the dinner party at which it is claimed Mr Yushchenko was poisoned
But witnesses and experts Newsnight has spoken to have cast doubt on whether Yushchenko could have been poisoned at that dinner.
Mykola Katerinchuk, an MP and friend of the Ukrainian leader said: "It would have been too obvious, too unprofessional".
And Alistair Hay, professor of environmental toxicology at Leeds University in the UK points out that dioxin does not normally cause severe gastro-intestinal damage as suffered by Mr Yushchenko.
The likelihood is either that Mr Yushchenko ingested a cocktail of poisons, or that he was poisoned earlier than is generally thought - and possibly on several occasions.
The inquiry still seems a long way from the truth. No one has yet been arrested and Newsnight has learned that some key witnesses have not been formally questioned.
But it has the potential to provoke a serious political rift between Ukraine and Russia - two countries that now say they want to work together again.
Tim Whewell's film was broadcast by Newsnight on Tuesday, 22 February, 2005.
Newsnight is broadcast every weekday at 10.30pm on BBC Two in the UK.
Newsnight was 25 on 30 January, 2005. Click on the link on the right-hand side of this page for more on the show's history.