Under the cover of darkness, the two officers made it safely away from the tracks and sought help. They were hidden in the belfry of a church by a French priest, then connected with a French resistance leader named Georges Le Coz. He turned out to be an unsavoury individual bent on evil.

Dr. Fairweather said that he and Mr. Veness initially stuck with Le Coz because he appeared to be a smart “survivor.” But his brutal nature soon became apparent. Over the next two months, the Canadians witnessed Le Coz take mistresses, raid private chateaus for wine, money and food, and routinely shoot French citizens on the pretext that they were collaborators. They also saw him order the shooting of a handful of his own men after he accused them of attempting to desert with their rifles and ammunition.

One day, after Le Coz’s men had killed 11 Germans and taken several others prisoner, Dr. Fairweather watched in horror as the dead were arranged in a semi-circle, then propped in the sitting position with a bottle of wine placed in one hand, a loaf of bread in the other and a cigarette in each mouth. Le Coz’s men then danced gleefully around the arrangement of corpses.

On another occasion, after seizing a castle in Loches, Le Coz lined up some of the town’s citizens, including a police officer named Alfred Hangouet, and asked the Canadians to shoot him. The two Jacks refused.

“We said: ‘Our enemy is the Germans. We’re not getting into French politics,’ ” Dr. Fairweather said in 2007. “And he was quite irate about it, and stormed around. It was in the center of town. These people were all lined up. Some were just shot out of hand.”

After the Loches killings, Dr. Fairweather and Mr. Veness decided they should try to leave Le Coz’s group at any cost. They managed to contact a genuine underground unit, which helped them escape to England. After declining an offer to be sent home, they rejoined their North Nova units.

“I’m sure we wouldn’t have survived without the underground,” Dr. Fairweather said. “They protected us.”

Dr. Fairweather had nearly forgotten the 1944 afternoon when he saved a French police officer from death. Then, three years ago, he received a letter of thanks from the man’s daughter, Jeanine Wallace. She told him her father never forgot the heroic action of the two Canadians.

In the 1970s, a friend told Ms. Wallace of the book “The Two Jacks.” She recognized the protagonists as the two men who had saved her father, but did not know how to reach them.

In 2003, Mr. Veness died and his obituary appeared in The Globe and Mail. Browsing the Internet, Ms. Wallace came across the article, which quoted Dr. Fairweather and noted that he lived in Lewisburg, Pa. She wrote to him.

It was then that Dr. Fairweather learned the truth about Le Coz. He was a career criminal named Georges Dubosq. In the final years of the war, she said, it was common for people such as Mr. Dubosq to take advantage of the chaos and lack of civil authority to pose as resistance fighters. Her father had been investigating Mr. Dubosq when the criminal turned on him. When peace returned, Mr. Hangouet arrested him and he was executed in the fall of 1945 on charges of murder and treason.

Dr. Fairweather felt touched to receive Ms. Wallace’s letter and wrote back, joking that his role in saving her father made him her honorary uncle. The next time Ms. Wallace wrote, she called him “Uncle Jack.”

While honoured to receive France’s highest award, Dr. Fairweather spent little time thinking about the war and did not consider his actions heroic, said his wife, April Fairweather. “I just got lucky,” he told her. “I was at the right place at the right time. Anyone else in my shoes would have done the same thing.”

From New Brunswick to Lewisburg

Jack Fairweather was born in Rothesay, New Brunswick, in 1924. His father, Jack Fairweather, was a New Brunswick lawyer who later became a judge. His brother, Gordon, followed in their father’s footsteps and studied law, eventually becoming the province’s attorney-general and the first chief commissioner of the Canadian Human Rights Commission.