The film opens in Munich, Nazi Germany. It is 1938 and Nazi Brown Shirts invade the home of a young Jewish girl, Elsbeth, and kill her parents.

The film continues in Strasbourg, France (near the German border), where Marcel Marceau works unfulfilled in his father's butcher shop, disconnected from Nazi atrocities and eager for the arts, especially mime and painting. During 1939, as Nazi power consolidates and World War II approaches, Marceau performs a cabaret impression of Charlie Chaplin, using the narrow moustache also favoured by Adolf Hitler. Visual similarities between Chaplin and Hitler frequent the film. Marceau's passion for theatre strengthens further after discovering his father secretly performs opera. 

While Marcel's cousin, Georges, involves himself with a Jewish arm of the French Resistance, Marcel and Emma fall in love. Marcel's father, who had fled Poland years earlier, supports his son and Emma joining the anti-Nazi resistance. It is a decision that defines Marceau's wartime experiences and brings tragic consequences for Marceau's father: arrested in 1944 he dies in Auschwitz during 1945. 

A Scout troop which Emma and Georges lead rescues 123 Jewish children whose parents were killed by Nazis. Marceau's mime skills improve as he helps entertain the orphans in a nearby castle. Bonds with Emma also strengthen. After Germany invades Poland in autumn 1939 their involvement deepens with the French Resistance. Adults distribute the Jewish children into smaller groups to minimise their visibility, some to local churches and others to Jewish families. Marcel and Emma maintain contact with Elsbeth. 

After 1941 Marceau's story intertwines with the menacing Klaus Barbie, who is seen beating to death a Nazi homosexual in Berlin. Barbie portrays the murder as Aryan purification. Barbie arrives in Lyon in 1942 during the Nazi occupation of southern France. His aim is eliminating the French resistance. Barbie operates by bribing collaborators and brutal executions in an empty swimming pool at Gestapo Headquarters. Later, Barbie gains notoriety as "The Butcher of Lyon".

Marcel and Emma also move to Lyon, with Alain, who narrowly evades capture during a Nazi sweep of Lyon's train station. Marcel helps Alain escape by burning a German soldier. Emma and Mila, her sister, are less fortunate. Captured during another Gestapo roundup, Barbie tortures Mila to death while extracting information from Emma about the resistance. Emma survives by collaboration but later attempts suicide-by-train. Marceau saves her and they resolve to help Jewish children escape to Switzerland.

Pretending their Scout troop is hiking, Marcel and Emma, accompanied by Alain plus a dozen children including Elsbeth, travel by SNCF train to the French Alps. Barbie and SS troops patrol the last train station before the Franco-Swiss border, forcing the petrified Emma into hiding as they search the train. Barbie fails to discover Emma or the children's true ambition to reach Switzerland. Marcel and Emma continue their journey towards Switzerland with the children.