Kizza Besigye hunches forwards in his seat. Elbows propped on his knees, hands clasped, gaze fixed forward. "There was a moment, vivid in my memory, when I saw that the man in front of me was dishonest," he says of a former friend. "It was traumatic to me. I had invested a lot of faith in him and what he said he stood for. I had held him in such high esteem, and realised it was false."
He is talking about Uganda's president for the past 25 years, Yoweri Museveni, who was sworn in for another five-year term last week.
Besigye, the country's most popular opposition leader, was Museveni's field doctor during the bush war that brought him to power. But they have been bitter enemies for more than a decade. For the past month, a string of protests dubbed "Walk to Work", have seen Besigye, their figurehead, dominate the headlines in East Africa and beyond.
It has been something of a resurgence for the Ugandan opposition, which was widely considered a spent force after February's general elections. Besigye, runner-up in the presidential race, polled only 26 per cent of the vote. When the opposition leader called for protests that month, alleging massive vote-rigging and buying, few listened.
Museveni is still popular. Though electoral observers pointed out flaws, none asked for a rerun, and most diplomats in the capital Kampala agreed that – though there was certainly rigging – Museveni's victory probably reflected the will of the Ugandan people.
"The man in the hat" as Museveni is sometimes called, is respected both in Uganda and outside for bringing growth to a country broken by war, for fighting Islamists in neighbouring Somalia and for securing relative peace and stability to this once chaotic country.
But the recent protests have escalated quickly in both intensity and popularity, spurring the most significant political unrest in Sub-Saharan Africa since the advent of the Arab Spring.
And Museveni's response has been unpopular. The crucial impetus behind the escalation has not been any initiative of Besigye's party, the Forum for Democratic change (FDC) or of the group that initiated the demos, Activists for Change (A4C), but the violent reaction of the state's security forces.
The protests were intended as peaceful demonstrations against the unchecked rise in food and fuel prices in Uganda, with opposition MPs and leaders leaving their cars at home each Monday and Thursday, to walk to work.
When Besigye set out to walk on the first day of protests, he cut a fairly unthreatening figure and some in his party worried that few would take notice. But the police changed that.
He has now been arrested four times, and hospitalised twice. During the most recent arrest, he was temporarily blinded and badly bruised after plainclothes security operatives doused him in pepper spray and dragged him, semi-conscious, into a police pick-up truck.
The police brutality he has encountered is a reflection of the President's "immense fear of losing power", says Besigye, who says he takes part in the protests to "stand with the marginalised sections of society in this time of difficult conditions for survival", referring to the food and transport inflation in this poor East African country, "with the objective of energising them to demand better".
The day after Besigye's latest arrest on 28 April, riots rocked the capital and two other cities, leaving nine dead and hundreds injured, according to Human Rights Watch. Besigye was flown to Kenya, where he received two weeks of treatment in a Nairobi hospital.
He returned last Thursday, eyesight nearly intact, overshadowing the pomp of his rival's fifth inauguration as tens of thousands of jubilant supporters surrounded his convoy.
The 45-minute commute from Entebbe to Kampala lasted all day. In an effort to disperse his supporters, police and military fired water-cannons, tear gas and, ultimately, live ammunition, killing at least one.
In the sitting room of his beautiful Kampala home, barefoot Besigye looks more the bespectacled medical doctor than the political leader or guerrilla warrior. He is a big man, with a crudely drawn face and the gruffest rumble of a voice, but he speaks in an intellectual's measured language.
Orphaned at an early age, Besigye earned a medical degree in his mid-twenties, and was a junior minister in the new NRM government by his early thirties. He has been the only credible challenger for the presidency since then, but he denies he is ambitious.
"I wanted to become a medical doctor, to simply assist in delivering healthcare to our people. I had never had political ambitions," he says.
"I have offered myself three times as a presidential candidate but it was never my mission. My mission has always been to have a just and fair democratic political dispensation in this country. And if there was, I would never have wished to be involved in the contest."
He calls himself "an activist in a liberation struggle", not a politician, and says the years since he lost faith in Museveni and his government have proven him right with the state becoming progressively more dictatorial, manipulative and corrupt. His own support base is difficult to measure. But the popular desire for change, he says, is certainly much more pronounced than the results of previous elections have shown.
He grows animated as he draws a parallel between his own country and Egypt, arguing that the popular revolution that ended the long reign of Hosni Mubarak earlier this year could not have been predicted based on electoral statistics. "All repressive regimes make it difficult for people to express their true feelings towards the government."
If he was to take the presidency from Museveni, Besigye thinks he would position himself as the manager of the transition from dictatorship to democracy. "There are institutions that would need strengthening, systems of government that need to be made to function."
But he is almost sure he won't run again. "I will not be offering myself," he says. "People have been sufficiently awakened to demand a better dispensation."
The man at the centre of what is becoming one of the world's most under-covered political crises does not know how long the protests will continue. But what he does know is that there are only two possible endgames. The first is that the government negotiates with the protesters and paves the way for a transition to a more democratic system.
The alternative is starker: the government will crumble. "An intransigent regime will collapse under the weight of illegitimacy, with all its sources of power exhausted and consumed," he says, before slipping back into his restful weekend. But he plans to walk again on Thursday.