The setting was an 18th-century villa on the shores of Lake Geneva, for a buffet lunch featuring almond trout and sable fish. Sometime after the trout had been consumed, and as the delegates filtered out into the gardens, the US diplomat William Burns and the Iranian chief nuclear negotiator, Sayeed Jalili, sidled off to a side room for a tête a tête.
In diplomatic parlance, such encounters are called "bilaterals" and they happen all the time. For three decades however, they have not happened, at least officially, between Americans and Iranians. So even if the men chatted about nothing more significant than the Alpine view, or the trout, the half hour together was imbued with historic symbolism.
As it happens, Burns reportedly used the meeting to reinforce Barack Obama's demands on Iran's nuclear programme and his offer of dialogue and to raise concerns about human rights following the June presidential elections.
The two men would appear to have little in common. Burns is an unflappable career diplomat, nicknamed "food processor" because he is such a smooth operator. He has worked with presidents going back to Ronald Reagan and in foreign postings around the globe.
Jalili is 44, lives in a modest house in Tehran and drives a battered Kia Pride. But Iran's point man in the nuclear stand-off with the West is not exactly a humble civil servant. The former university lecturer is extremely close to President Mahmoud Ahmadinejad and has been identified (by the former president Ali Rafsanjani) as one of four chief architects of his election "victory" in June and the vicious crackdown on dissidents and reformists that followed.
Jalili is young by Iranian standards to hold the role he does. He was parachuted into the job by Ahmadinejad two years ago, a reflection of his standing in the hardline conservative cabal that surrounds the President.
He is ultra religious – so much so that staff in the Foreign Ministry, where Jalili rose to prominence, were surprised by the standards of observance that he expected of his underlings. Like Ahmadinejad, Jalili is rumoured to believe in Mahdi, the so-called 12th or "Hidden" Imam, who according to doctrine, will return to save his followers in a "time of cosmic chaos".
Western diplomats, used to the smooth, urbane Ali Larijani, have apparently been horrified by his successor's hardline attitude. At a meeting last year, Jalili regaled his Western counterparts with a two-hour history of British and American perfidy, from the 1953 coup which brought the Shah to power, through the 1980-88 Iran-Iraq war, of which he, like Ahmadinejad, is a veteran. (He still walks with a limp from his wounds.)
Yesterday, perhaps mollified by winning "face time" with the man from Washington, his address to gathered diplomats covered much of the same historical ground – but wrapped up a lot quicker.