By GINGER THOMPSON

WASHINGTON — She was twice divorced and fresh out of South Dakota when she fell for his worldly sophistication. He came from one of this city’s most privileged families, and admired her work helping ordinary people.

Together, Gwendolyn and Kendall Myers set out to give the second half of their lives new meaning. At first, disillusioned with the pace of change in Washington, the great-grandson of Alexander Graham Bell, who at the time was a State Department contract employee, and the housewife turned political activist moved to South Dakota, where they embraced a counterculture lifestyle, even growing marijuana in the basement. They marched for legalized abortion, promoted solar energy, and repaired relations with six children from previous marriages.

When the wide-open spaces of the West quickly grew too small, the couple returned to Washington a year later, renewing their ties to the establishment that they had rejected.

But the government says the real reason for the Myerses’ 1980 return was to spy for Cuba. In a complaint that reads in parts like a novel, federal prosecutors allege that Mr. Myers, now 72, used his top-secret clearance as a State Department analyst to steal classified information from government files for nearly three decades, and that Ms. Myers, 71, who worked as a bank clerk, helped pass the information to Cuban handlers. They were arrested earlier this month and are being held without bail.

The strongest argument in support of the government’s case may have been made by the Myerses themselves. In the 40-page complaint they are quoted telling an undercover F.B.I. agent how much they admired Fidel Castro, how they sent secret dispatches to Havana over short-wave radio, dropped packages to handlers in shopping carts at local grocery stores, traveled across Latin America to meet with Cuban agents and used false documents to travel to Havana for an evening with Mr. Castro.

American officials say they are still trying to determine what secrets were stolen and the consequences for the nation’s security.

It appears that the Myerses were not motivated by money. The authorities said that other than being reimbursed for equipment, the couple were not paid for spying. On the contrary, according to the statements cited in the complaint, which one federal magistrate said made the case against the couple “insuperable,” the couple felt disdain for America’s foreign policy — Mr. Myers’s diary described watching the television news as a “radicalizing experience” — and a romanticized view of Cuba’s Communist government.

And, just months after Mr. Myers’s retirement supposedly ended the scheme, they hinted that spying provided adventure to what seemed to have otherwise been a relatively mundane life. “We really have missed you,” Mr. Myers said in April to the undercover F.B.I. agent who was posing as a Cuban intelligence official. “You, speaking collectively, have been a really important part of our lives, and we have felt incomplete.”

The arrests of Mr. and Ms. Myers, who have been held without bail since their arrests earlier this month, made headlines around the world and ignited a flurry of messages between Miami and Havana. Prosecutors have refused to speak about the continuing investigation.

Meanwhile, the couple’s friends and relatives from Washington to South Dakota are still in shock over the allegations.

“When the F.B.I. came to the door and told me my mother had been arrested, I kept thinking they must have the wrong house,” said Ms. Myers’s daughter, Jill Liebler, 52.

“The media has painted a picture of him as a loner, a zealot, a man with an agenda,” said Michael Myers, referring to his father. “That’s not who he is.”

But others acknowledged that there were glimpses of the couple they knew in the portrait painted by the government.

Jay Davis, a public defender in South Dakota, remembered a weekend years ago at a mineral bath resort, where Cuba was about all that Mr. Myers talked about. “He made it sound so wonderful, I started thinking seriously about going,” Mr. Davis recalled.

Court documents say that Mr. Myers, an expert on European history, became interested in Cuba in 1978. Divorced, he immersed himself in world affairs as an adjunct professor at the Johns Hopkins University School of Advanced International Studies and a contract instructor at the State Department’s Foreign Service Institute.

According to the complaint, Mr. Myers was invited to Havana by an unnamed Cuban official who had made a presentation at the institute. The trip, according to Mr. Myers’s diary, had a profound effect on him.

Going through the Museum of the Cuban Revolution in Havana “was a sobering experience,” Mr. Myers wrote about the trip in his diary. “Facing step by step the historic interventions of the U.S. into Cuban affairs, including the systematic and regular murdering of revolutionary leaders, left me with a lump in my throat. They don’t need to try very hard to make the point that we have been exploiters.”

Meanwhile, Gwendolyn Steingraber was getting her own crash course in world affairs as an aide to Senator James Abourezk, a South Dakota Democrat who was one of the leading proponents for ending the United States embargo against Cuba.

A homemaker and a mother of four, she had been swept up in Senator George McGovern’s anti-Vietnam War movement of the Democratic Party and began volunteering in political campaigns.

On Capitol Hill, she held a low-level job — mostly involving outreach to constituents — in the shadows of rising political stars, including former Senator Tom Daschle and Pete Rouse, who is a top adviser to President Obama. Former colleagues described her as bright, a bit naïve and lacking the savvy and formal education — she did not attend college — to move up the career ladder.

“It wasn’t the most important job in the office,” recalled Wendy Grieder, a former legislative aide. “But to Gwen it was the big time.”

Peter Stavrianos, another former colleague, added, “She was not remarkably different than dozens and dozens of other people that you ran across in the 1970s who were McGovernites that got into politics for reasons other than to make a lot of money.”

Mutual friends introduced Mr. Myers and Ms. Steingraber, who soon became inseparable.

“I have yet to meet a couple who are more in love than the two of them,” said Amanda Myers Klein, 40, Mr. Myers’s daughter. “They are beautiful together.”

In 1979, Mr. Myers, then 42, followed Ms. Steingraber, 41, to Pierre, S.D., where she got a job at the Public Utilities Commission helping farmers use alternative energy. He worked on a biography of Neville Chamberlain, the British prime minister, whom Mr. Myers admired for his policies toward the Nazis.

He also tried to make the best of living in the small town of 10,000 — camping, gardening, writing and hanging out at the truck stop talking politics with local farmers. Still, to people who knew him, it seemed clear that Mr. Myers would never fully fit in.

“They were different than what we were used to seeing in South Dakota,” said Greg Rislov, who still works at the utilities commission. “They dressed different. They lived different. There was no question in my mind that Kendall, with his Ph.D., was looking to do more than sit in a small house in Pierre all his life.”

Less than a year after the Myerses arrived, neighbors said, police officers raided their home and seized the marijuana plants in the basement. And soon, the election of a Republican governor cost Ms. Myers, a political appointee, her commission job.

Investigators said a Cuban intelligence agent visited the couple and suggested that they return to Washington to work as spies.

They moved back in 1980 and married two years later. Covertly, according to investigators, Mr. Myers became Cuban agent 202. She became agent 123. The complaint against them said he would either sneak documents out of the State Department or memorize information and write it down at home. Investigators said he gained access to at least 200 sensitive or classified reports pertaining to Cuba between 2006 and 2007. Meanwhile his wife would pass information along to Cuban contacts.

The F.B.I. warned the State Department in 2006 of a suspected mole in the agency. In what could turn out to be a significant coincidence, that was the same year that Mr. Myers drew attention for his political views.

In a speech at the university where he taught, he derided the so-called special relationship between the United States and Britain as a myth, and said that President Bush had duped Prime Minister Tony Blair into supporting the Iraq war.

The speech received extensive coverage in the British press, and prompted the State Department to issue a strong repudiation.

“His was not the measured, balanced presentation you might expect of a State Department official,” said Robin Niblett, a specialist on Europe who spoke at the same event.

By the time the F.B.I. caught up with the couple, Mr. Myers had retired from the State Department and was working part-time as a teacher at the School for Advanced International Studies. But according to the complaint, when an undercover agent posing as a Cuban spy greeted Mr. Myers with a cigar after class, the thrill of espionage returned.

He and Ms. Myers later met the agent in a hotel room, and said they did not want to resume full-time spying, but would be willing to work as a “reserve” force, the court document said. And they said they looked forward to sailing away to Cuba, which they referred to as “home.”

“We really love your country,” Mr. Myers told the agent, according to the complaint. “The people and team are just important in our lives. So we don’t want to fall out of touch again.”

Margot Williams, Kitty Bennett and Barclay Walsh contributed research.