In Rome shortly after World War II, British Col. Michael "Hooky" Nicobar (Walter Pidgeon) is expecting a transfer home when he is instead posted to Vienna with his aides Junior Commander Audrey Quail (Angela Lansbury), Major John "Twingo" McPhimister (Peter Lawford) and Sergeant David Moonlight (Melville Cooper).

Catlock (Robert Coote) in monitoring possible "subversive activities" against the Allied nations and repatriating Soviet citizens living in the British zone of Vienna.

Hooky is reproved for his rigid obedience to duty by Twingo and the Mother Superior but angrily shifts responsibility for what happened to the nun.

When Piniev's aide tells Hooky that Bruloff's suicide was proof of "subversive activity and treasonable behavior," he starts to doubt the sincerity of the Soviets.

On Christmas Eve, after the Mother Superior asks for his forgiveness for not treating him in a Christian manner, Hooky tells her that he lost his faith after the death of his son in combat.

Hooky upbraids the Soviets for their ploy, telling them he knows they staged the incident because they have no use for people too old or too young or too weak to work and are dumping them on the British.

The next day, in response to his brief, Hooky is ordered to fly to Rome as a representative to a United Nations conference to end forcible repatriation, and helps Mother Superior join him to see the Pope on the same issue.

Meanwhile, Twingo and Maria plan on moving to Scotland, when she is suddenly captured by Hooky's replacement, the pompous and rigid Colonel Omicron, who intends to turn her in to Piniev.

Shortly after the release of the novel Vespers in Vienna, Metro-Goldwyn-Mayer showed interest in a film adaption and production was set to start in June 1947.