His wife Nazanin Zaghari-Ratcliffe and the couple's 22-month-old daughter Gabriella had been on holiday visiting family in Iran and were due to fly home to Britain on April 3.
But they never made the flight.
Zaghari-Ratcliffe, a dual British-Iranian citizen, was arrested at airport check-in in Tehran, according to her husband who has spoken to her family in Iran. Ratcliffe fears his wife is in solitary confinement.
Their child Gabriella, who has British citizenship only, had her passport confiscated by authorities, and remains with her grandparents in Tehran, said Ratcliffe.
Zaghari-Ratcliffe, 37, a project co-ordinator with the Thomson Reuters Foundation, a charitable arm of the international news outlet Thomson Reuters which supports independent journalism, has been unable to visit her daughter or access a lawyer since being taken to an unnamed prison, added Ratcliffe.
However, authorities have now told Zaghari-Ratcliffe's family in Iran that they will be able to visit her Wednesday, said Ratcliffe.
Zaghari-Ratcliffe has been allowed to make some phone calls to her family in Tehran, according to her husband. She told them she was made to sign a confession under duress -- though its contents are unknown.
She has not been able to speak to her husband since her arrest.
Ratcliffe says they have not been told by Iranian authorities why his wife was arrested -- only that there "was a serious investigation around an issue of national security."
The Iranian Foreign Ministry said it had no information regarding Zaghari-Ratcliffe, and the Iranian Embassy in London has not responded to CNN's requests for comment.
A UK foreign office spokeswoman told CNN: "We have been providing support to the family of a British-Iranian national since we were first informed of her arrest, and will continue to do so."
The Thomson Reuters Foundation said Zaghari-Ratcliffe had worked with the organization for the last four years, adding that she had no professional dealings with Iran.
"In fact, Thomson Reuters Foundation has no dealings with Iran and does not operate in the country," it said in a statement. "We cannot understand the reason for her detention and hope the matter will be resolved as soon as possible."
"It's really been disorientating, and terrifying, and just incredibly confusing," Ratcliffe said of the family's month-long ordeal.
"I've heard people speculate that the arrest may have something to do with her charity work," he said. His wife trains journalists in developing countries such as Morocco and Burma, though she's never worked in Iran for the Reuters foundation.
"Other people have speculated that it may be because she has dual passports," he continued.
Iran doesn't recognize dual citizenship, which means Zaghari-Ratcliffe is only recognized as Iranian, and as such is prevented from accessing British consular assistance.
The International Campaign for Human Rights in Iran told CNN that it was aware of at least five other dual national imprisoned in Iran.
These include Iranian-Americans Siamak Namazi, a businessman who has been held since October last year, and his 80-year-old father Baquer Namazi, who was arrested in February.
In desperation, Ratcliffe, a 41-year-old accountant from north London, has now decided to go public with the story -- against the advice of the UK Foreign Office.
Ratcliffe has launched a petition
calling on British Prime Minister David Cameron — and Iran's Supreme Leader Ali Khamenei -- to help free his wife. It has received over 84,000 signatures at time of writing.
"When you hit 30 days it's an awful long time," said Ratcliffe of remaining silent until now. "Let's see what the authorities' response to going public will be -- if it backfires, then that will be on my shoulders."
Zaghari-Ratcliffe moved to Britain in 2007, and has visited her family in Iran four times since having baby Gabriella almost two years ago, Ratcliffe said.
Without a visa, Ratcliffe says he is reluctant to travel to Iran. But he vowed: "I'm not going to leave Gabriella there for months and months without her mommy."