During the course of the war, Lindell was run over by an automobile, shot in the head, imprisoned twice, and captured and sent to Ravensbrück concentration camp in Nazi Germany.

Outspoken, controversial, and imperious, Lindell was called a "false heroine" by one critic, but she is credited with helping about 100 Allied airmen escape from France.

She advocated successfully with her German captors for the release of 47 American and British women to the Swedish Red Cross in the closing days of World War II.

[3] During the First World War, she served as a member of the Voluntary Aid Detachment (VAD) and subsequently with the Secours aux Blessés, a division of the French Red Cross.

Lindell, her children, and Michele Cambards, teenage girlfriend of her son Oky, began escorting soldiers and airmen by train from Paris to Sauveterre.

The people she escorted across the border into Vichy France were subsequently helped to return to the United Kingdom by the Pat O'Leary escape line and the Seaman's mission of Donald Caskie in Marseille.

George Whittington, an American Vice Consul in Lyon, France, obtained for Lindell an exit visa from Vichy, describing her as a "stranded English governess."

MI9 officer, James Langley said of her, "Mary was a very brave, courageous woman who wanted to have everything her own way...she was, to put it mildly, difficult...she wouldn't obey any instructions given by us"[11] Nevertheless, Lindell was accepted and became one of two female agents sent to Europe by MI9, the other being Trix Terwindt who was sent to the Netherlands.

Ill, bandaged, and with her arm still in a sling, she assisted two of the best known escapees of World War II: Herbert Hasler and Bill Sparks, the "Cockleshell Heroes" and only survivors of Operation Frankton.

Her daughter Barbé (who was friends with many of the German occupiers of Paris) negotiated a bribe of 60,000 francs for Maurice's release with Klaus Barbie, the notorious Gestapo leader.

She made enemies, refusing to accede to demands by a British intelligence officer that he be evacuated immediately, telling him "this is an escape route for airmen."

She was wearing, as usual, her Red Cross uniform and was awaiting the arrival by train of four airmen whom she planned to send with a guide across the nearby Pyrenees to Spain.

[20] In August 1944, with the liberation of France by Allied forces underway, Lindell and three other women were transported to Ravensbrück concentration camp in Germany, arriving there on September 3, 1944.

From her job at the hospital, Lindell had the opportunity to meet or hear of many of the British and American women and made a list of those imprisoned at Ravensbrück.

[23][6] In 1945, during the closing months of World War II, a Swedish diplomat, Folke Bernadotte, negotiated with the German government for the release of women prisoners from Ravensbrück and other concentration camps.

Lindell, ill from pneumonia, claimed that she rose from her hospital bed and confronted the camp commander, SS officer Johann Schwarzhuber.

She also criticized the judge advocate, "who was partial and objectionable, had taken on the cross examination of witnesses himself and prevented other questions from being put which might have been [answered] in favour of the accused.

[29] In 2015, Marie-Laure Le Foulon published an account of her research on Lindell based on the work of Corinna von List and information provided by Anise Postel-Vienay, both members of the French Resistance.

[33] The 1991 film One Against the Wind starred Judy Davis, and was based on the biography Story of Mary Lindell: Wartime Secret Agent by Barry Wynne.