They are listening to a private lecture by Habibollah Peyman, a teacher at Tehran University. An unassuming man of slight frame, he was born a political fighter. Imprisoned for five years by the Shah, his students were later active in the overthrow of the monarchy. Today Dr Peyman is telling a new generation of students to fight for greater freedom. He condemns the clergy for turning Iran into a totalitarian state.
While such talk is never heard openly in Iran, there is a growing dissent from the country's religious intellectuals. Dr Peyman is not criticising the government from a Western or secular perspective. He is attacking the regime on its own terms. And that is why he is more dangerous to the ruling clergy than foreign or liberal opponents.
Dr Peyman is one of a group of Islamic scholars who have become known as the "New Thinkers". Their intellectual challenge is shaking the foundations of the Islamic faith and their thoughts will have implications for Islamic movements throughout the world.
The New Thinkers are building an Islamic ideology that can deal with the 20th century. They want to show that an Islamic government can break the closed circuit that prevents it entering the modern era and relating freely to the outside world. Peyman is challenging 13 centuries of thinking - that a literal interpretation of the Koran is the mark of a true believer. He accuses Iran's mullahs of being incapable rulers, unable to govern effectively. "The clergy have failed to fulfil the promises of the revolution and this has placed the legitimacy of their entire political system under question," he says.
For a first-time visitor to Iran, the country does not conform to its image. With its wide, tree-lined boulevards, Tehran is not the dark brooding city imagined by Westerners. There is also a surprising level of debate. Unlike most of Iran's Arab neighbours, fear of the regime does not run so deeply as to prevent criticism and discussion.
But after a few years of tentative opening, the boldness of men such as Dr Peyman has led to a fresh clampdown. It began last October with the writer Abdol Karim Saroush, one of the first New Thinkers to speak out. His lecture at Tehran University was broken up and he was forced into hiding. Saroush argued that if 7th century Islam is used as a modern political ideology, it will become totalitarian and will ignore the interests of the people. The conclusion: that enforced religious rule and democracy are incompatible.
The religious hardliners are worried. Their response has been to beef up their loyal foot soldiers, the Bassidj, or the Mobilised Force for the Oppressed. These men are the private army of the ayatollahs, based in mosques throughout Iran. Their loyalty is to the religious leaders, not the politicians. Allah Karam is one of the fiercest members of the Mobilised Force. He organised the attack on Abdol Karim Saroush's lecture. I met up with him as he toured schools seeking recruits. During the war with Iraq, the Mobilised Force provided the suicide squads who walked on minefields to achieve martyrdom. The soldiers of the Mobilised Force, he said, "will fight until our last drop of blood" to combat those who talk of "the separation of mosque and state".
The most worrying aspect for the hardliners is that some members of government are following the New Thinking. Iran has had years of economic mismanagement and stifling bureaucracy. Corruption and cynicism have become commonplace.
The values that inspired the revolution are sneered at. There is a consensus that the mullahs cannot deal with a modern, complex economy.
President Rafsanjani has realised that for the regime to survive, it must control the economic free fall and the slide into debt. His government has brought in various experts and specialists. Mostly with foreign, indeed American education, they are detested by the clergy and the Mobilised Force. Technocrats are responsible for building American-style supermarkets in Tehran, and gaudy consumerism is being tolerated in the interests of economic progress.
One of the President's closest advisers is Morteza Alviri. A one-time hardliner, he is now a supporter of laissez-faire economics. "We have arrived at a decisive moment in the history of the Islamic Republic," he told me. "We must move towards an open economy, and that requires an open political system."
Next month's parliamentary elections will be far from free - opposition parties have been banned from standing - but they will reflect a genuine debate over Iran's destiny. The results of the poll will be a vital indicator of whether Alviri and other reformers can continue their policies. The strategy of managed, gradual openness pioneered by Rafsanjani is being tested. But the unspoken issue being fought over in the election goes to the heart of the Islamic Republic itself: should the clergy retain the divine right to rule? The mullahs know that the logic of the reformers' arguments will undermine their privileges and their authority to govern. They want a pure Iran, free from Western values.
Dr Peyman doubts that there will be any lurch toward openness. He told me how both the reformers and hardliners had watched events in the former Soviet Union and elsewhere in eastern Europe. "They saw what happened when a government lifted restrictions and gave freedom. People ceased to fear government, and the result was the collapse of the whole system."
Hardliners are aware that the battle lines over the future destiny of Iran are drawn. But they also know that if the clamour of dissent from the New Thinkers becomes too loud and gains popular support on the streets, they have an answer. Allah Karam and the Mobilised Force will be there to restore fear and impose the will of the Ayatollah.
8 Phil Rees's film, 'Guardians of the Ayatollah', will be shown on BBC2 at 7pm on 28 February.Reuse content