In 1999, an 87-year-old British woman held a press conference in front of her home to announce that for nearly four decades, she’d worked as a spy for the Soviet Union.

In fact, Melita Norwood was the Soviet Union’s longest-serving British spy. From World War II through the Cold War, she stole nuclear secrets from the office where she worked as a secretary and passed them to Moscow.

Norwood was coming clean because a Cambridge historian had discovered her espionage while writing a book, but she was unrepentant. She told The Times of London that “in the same circumstances, I know that I would do the same thing again.”

Norwood was a long-time member of the Communist Party who supported the Soviet Union’s attempt to bring communism to Eastern Europe and feared a world in which the United States and Western Europe held unchallenged nuclear power. She began her spying career in the 1930s while working as a secretary for the Non-Ferrous Metals Research Association in London.

This innocuous-sounding association was actually part of a secret nuclear weapons research project with the U.S. called “Tube Alloy.” When no one was looking, Norwood would sneak into her boss’ office, open his safe and take pictures of the secret documents inside. She’d then pass the camera off to her contact in the KGB, who knew her by her code name “Hola.”

Experts still debate how much she actually ended up helping the Soviet nuclear program. But she continued to send these secret files until the early 1970s, when she retired as a spy. In 1979, she and her husband—who knew about her spying and disapproved—visited Moscow so the Soviet Union could award her the Order of the Red Banner (she accepted the honorary award, but turned down the financial reward).

How did Norwood get away with it for so long? Well, she was partly aided by the boys’ club atmosphere of MI5, the British Security Service. Mona Maund, one of the first female MI5 agents, actually identified Norwood as a possible spy back in the 1930s, when Norwood was at the beginning of her espionage career. But a male superior dismissed her tip because he didn’t think women could be good spies (in 1940, he fired Maund for accusing him of incompetence). Though Norwood’s employers were suspicious of her ties to the Communist Party, over decades of work they never pinpointed her as a mole.

British intelligence only confirmed she was a spy in the 1990s after the fall of the Soviet Union, when the former KGB officer Vasili Mitrokhin defected to the United Kingdom and turned over six trunks of archive information about Soviet spying. These documents revealed Norwood’s espionage, but British officials kept it secret because they didn’t think there was enough evidence to prosecute.

In 1996, the government decided that the information in the Mitrokhin papers should be available to the public, and handed them over to the Cambridge professor Christopher Andrew so he could write a book about them. Norwood’s secret finally came out in September 1999, when The Times of London began to publish Andrew’s book serially.

The revelations came as a total surprise to Norwood's daughter, Anita Ferguson, who didn’t find out her mother was a spy until she read about it in the paper. As the news of Norwood’s espionage broke in The Times, Norwood held a press conference to confirm that she was a spy and explain why she’d done it.

“I did what I did not to make money but to help prevent the defeat of a new system which had, at great cost, given ordinary people food and fares which they could afford, a good education and a health service,” she told the press in front of her home. “I thought perhaps what I had access to might be useful in helping Russia to keep abreast of Britain, America and Germany.” She added that, “in general, I do not agree with spying against one's country.”

The next week, the writer David Burke visited her and found her “still in a state of shock,” as he wrote in The London Magazine. Burke, who later wrote The Spy Who Came In From the Co-op: Melita Norwood and the Ending of Cold War Espionage, noted that Norwood kept repeating “I thought I’d got away with it.” Yet as Burke wrote, she actually did get away with it: even after her outing, the government still declined to prosecute her.

Norwood died in 2005, but people have remained fascinated with her story. In 2013, author Jennie Rooney published a novel, Red Joan, loosely based on Norwood’s life. And in April 2019, a film adaptation premiered in the U.K. and the U.S. starring Judi Dench as Joan Stanley, the fictional counterpart to Melita Norwood, the real-life spy.