Bing Crosby plays William Wainwright, a World War II correspondent stationed in Paris. There he meets, falls in love with, and marries a French singer, Lisa Garret (Nicole Maurey), a popular singer and, unknown to her husband, a secret member of the French Resistance. Soon a boy, Jean, is born to them. Assigned to report on the Battle of Dunkirk, Wainwright reluctantly leaves Lisa and the infant to cover the story.
Red tape prevents his early return to Paris. When he does, months later, he is stunned to learn that the Nazis executed Lisa. Many lyrics of her songs were encoded with secret messages to the Resistance, for example, "Mon Coeur est un violon." Finding it impossible to accept her violent death, he goes into denial, descends into bitterness, and returns to America.
The audience is given this information in a flashback as Wainwright, after the war, flies back to Paris in an effort to find his six-year old son (Christian Fourcade) who is reportedly living in a Catholic orphanage for young boys. The Mother Superior points out a scrawny-looking child, shy but intelligent, and he does resemble his mother.
A skeptical Wainwright takes the word of the crusty Mother Superior (Gabrielle Dorziat) who conveys certitude the boy is his son. She cautions however that he ought not become too attached to Jean. Wainwright begins to test Jean's memory through a series of experiences aimed at arousing his very early childhood memories. To advance the cause along, Mother Superior and others begin to create for the boy wrong memories about his childhood.
On discovering this trick, Wainwright registers anger at all concerned, including Jean. He arranges his return home to America without the boy. Embarrassed by his own silly deceptions, the youngster abandons hope of ever coming to America with "Monsieur" Wainwright and has rejoined his class at the orphanage.
Before departing Paris, Bill goes to the orphanage to leave for Jean a little stuffed dog he won at a local shooting gallery. Little does he realize that, before Jean's tragic loss of his mother, he had played with a copy of this very same toy he named Binky. Wainwright leaves the package on Mother Superior's desk and tells her it's for Jean. She sends for him. "Pour moi," he asks? She nods for him to open. He unties the string and sees the stuffed dog inside the brown paper. Instantly he cries out: "Binky, Binky!" He hugs and kisses the stuffed animal as he thinks that "Monsieur" Wainwright has found his long lost toy. Jean's automatic recall brings the film to an emotional and happy conclusion with the certainty that Jean is Bill Wainwright's son. Happily, gratefully, father and son leave the orphanage hand in hand.