Dr Kamiar Alaei is beautifully groomed and with impeccable manners. A man of charisma, he talks quietly and courteously. In conversation, you get the feeling you are the most important part of his day.
But his brown eyes hint at a store pile of trauma and anxiety.
The 37-year-old clinician is campaigning for his brother, Arash Alaei, 42, halfway through a six-year term in Tehran's notorious Evin prison.
Campaigners against Aids in Iran, the brothers were arrested in June 2008 and, after a summary trial, jailed for "communications with an enemy government" and seeking to overthrow the Government.
Kamiar received a three-year term; he served two-and-a-half years, 63 days of it in solitary, before being released late last year. His brother is still in jail, even though under Iranian law, first offenders are released after half their sentence.
"At night, my mind goes back to prison," Kamiar told the Herald.
"I spent 870 days there, 3800 hours. But I will never be free until my brother is free."
Last week, at a world Aids conference in Rome, leaders in the 30-year-old war on the pandemic issued calls for Arash Alaei's release.
He was detained "for the only reason that he was trying to treat HIV-positive people in his home country", said Elly Katabira, president of the International Aids Society , which staged the conference.
"There is no reason why HIV professionals around the world should be in prison only for doing their job, and we, all of us, demand his immediate release."
The case has also been taken up by Physicians for Human Rights, Amnesty International and Human Rights Watch. More than 3000 doctors, nurses and health workers from 85 countries have signed an online petition demanding his release. The brothers' pioneering work was rewarded with this year's Jonathan Mann Award, the most prestigious prize in the field of Aids.
From an upper-middle-class family, Kamiar said he became aware of the Aids stigma in 1997 while studying in Tehran.
He came across a 19-year-old man with HIV, "a tall, skinny guy from Azerbaijan", who had been dumped in a corner of the hospital, alongside his mother, by nurses who were terrified of the virus.
Intrigued, he trained in Aids medicine and set up a tiny community clinic which was crowded until late at night with people with HIV, many of them drug addicts, who had been rejected by almost everyone, including their families.
"After the clinic, every night I would go to their houses and talk to their families and say, he or she is a good person, not a bad person, but they have got HIV and need support. The families would cry, but the next day they would come to the clinic to ask for help."
At that time, HIV was widely seen in Iran as a "Christian disease", so the brothers approached educated religious leaders and asked them to relay safe-sex messages through mosques.
"At first, we had no idea what we should do," Kamiar explained. "We just wanted to help, so step by step we learned what was needed and, based on that need, we designed a programme."
The pair eventually set up clinics in 67 towns and cities, and scores more in prisons, established needle exchanges and methadone therapy, encouraged safe-sex education and lobbied the Government to fund free HIV drugs.
The work was urgently needed in a country where homophobia, ignorance and fear and punishment of drug users provide fertile ground for the Aids virus.
By 2005, the programme had been endorsed by the World Health Organisation as a "best practice" model. The Global Fund awarded it US$15.8 million to be administered by the United Nations Development Programme .
But things soured after Iran's reformist President, Mohammad Khatami, was replaced by the deeply conservative Mahmoud Ahmadinejad.
Zealots pinned homosexuality, drug addiction and prostitution on foreign influence. The two doctors were travelling extensively abroad to promote their clinics and attend conferences.
Their supporters speculate suspicions were roused in 2006 and 2007 by attendance at United States-Iranian meetings at the Aspen Institute, an NGO that fosters dialogue.
Unaware of the gathering storm, Kamiar moved to the US to study for a master's at Harvard. During a visit home in June 2008, he was seized, a day after his brother had been detained. He was stunned.
"I never ever thought we would be arrested. We never thought there would be a political dimension to our work," said Kamiar. "We had no motivation to be in politics because HIV is a health issue, it is beyond borders."
The trial lasted one day and took place behind closed doors, a process that rights groups decry as a witch hunt.
Kamiar glosses over the seven weeks he spent in solitary and his treatment by prison guards. He preferred to talk about his fellow inmates, ranging from prisoners of conscience to thieves and murderers.
"I continued my work in health education," he said. "I discovered they lacked a lot of basic knowledge, even hand-washing. We started a health programme, a fitness programme, exercises, volleyball.
"We taught prisoners to read and learn another language, and then got them to teach other prisoners in turn. We mobilised whatever resources we had. We painted the walls to try to make the prison a second home. They [the authorities] could not change it."
Facing an unpredictable regime, Kamiar chooses his words carefully, aware that even innocuous phrases could be twisted to delay his brother's release or cause him harm.
"It's difficult in my country," he sighed. "You cannot guess, you cannot predict. You never know what will happen. Maybe the next day you will be released. Then one day you will get arrested. It is hard."