Philippe Gerbier, the head of a French Resistance cell, is arrested by Vichy French police on suspicion of Resistance activity. Although he is acquitted due to a lack of evidence, he is still sent to an internment camp. He and a young Communist work on an escape plan, but before they can execute it, Gerbier is transported to Paris. While waiting to be questioned by the Gestapo, he manages to kill a guard and flee. In Marseille, Gerbier, Félix Lepercq, Guillaume "Le Bison" Vermersch, and Claude "Le Masque" Ullmann trick Paul Dounat, the young agent who betrayed Gerbier, into meeting them. They take him to a house, but discover the neighboring house is newly occupied, so they cannot use their guns to kill Dounat. Lacking a decent knife, they strangle their former associate. Félix meets his old friend Jean-François Jardie in a bar and recruits the risk-loving former pilot to join the Resistance. While on a mission to Paris, Jean-François visits his older brother Luc, a renowned philosopher who appears to live a detached, scholarly life. He then travels to the Mediterranean coast to help evacuate some Allied soldiers, along with Gerbier and the "Big Boss", to London via a submarine to Gibraltar. Jean-François does not recognize him in the dark, but the Big Boss turns out to be Luc, whose identity is a closely guarded secret. In London, Gerbier tries to arrange additional support for the Resistance from the Free French leadership, and Luc is decorated by Charles de Gaulle. When Gerbier learns Félix has been arrested by the Gestapo, he cuts his trip short and parachutes into the French countryside. After Félix's arrest, Mathilde, a Parisian housewife who is part of the Resistance, moves down to Lyon to run Gerbier's cell. Gerbier is impressed by her abilities, so he keeps her around. She devises a plan to rescue Félix, who is being tortured at the Gestapo headquarters. Jean-François, after hearing the details, writes Gerbier a letter of resignation and incriminates himself with an anonymous letter to the Gestapo so he will be jailed with Félix. Mathilde, Le Masque, and Le Bison try to rescue Félix disguised as Germans and with a forged order to transfer him to Paris, but their plan fails when the prison doctor pronounces him unfit for transport, as he is barely alive. When Jean-François, who has also been badly beaten, sees the rescue has failed, he gives Félix his only cyanide pill. Having seen Gerbier's picture on a wanted poster during the rescue attempt, Mathilde urges him to lie low, but he says there is no one who can take his place at the moment. He is swept up in a raid by Vichy police and handed over to the Germans. Taken to be executed, Gerbier and his cellmates are told that, if they can reach the far wall of a room before they are killed by machine gunners, they will be allowed to live a little longer. Once the shooting starts Gerbier runs to the wall, when suddenly Mathilde and Le Bison appear by a window and throw smoke bombs to block the Germans' view and a rope to help Gerbier. He climbs it and escapes with the group. Gerbier goes to hide out for a month in an abandoned farmhouse. One day, Luc arrives to discuss what to do about Mathilde, who has been arrested. He worries she will inform on her confederates, as her teenage daughter has been threatened. Luc hides when Le Masque and Le Bison arrive with the news that Mathilde is free and two members of the Resistance have been captured. Gerbier orders Mathilde's immediate execution, but Le Bison refuses to do so and swears to prevent Gerbier from killing her, so Luc emerges and convinces Le Bison that Mathilde would want them to kill her before she is forced to identify anyone else. Luc accompanies Gerbier, Le Bison, and Le Masque to Paris. They locate Mathilde on the street, and Le Bison shoots her twice before they drive away. Closing text reveals that all four men were captured and died within less than a year, either through suicide or at the hands of the Nazis. Gerbier's precise fate is succinctly described as "on 13 February 1944, he decided not to run this time".

Two Romanian orphaned young women, Voichița and Alina, visit a Romanian Orthodox convent during Lent, where Voichița tells Alina the altar includes an icon that grants wishes. Alina had been working in Germany, and the two girls were previously roommates at a children's home and had shared a physical relationship. The monastery is led by a 30-year-old Priest who speaks ill of declining faith in Western Europe, citing same-sex marriage, and forbids anyone outside of the faith from entering. He inquires about Alina to Voichița, who tells him Alina irregularly attends church and does not go to confession. They urge Alina to begin confessing. Alina hopes to sleep with Voichița, but Voichița tells her they must be cautious given it is Lent. Some time later after Alina has left the convent, Voichița retrieves her, but Voichița tells Alina she is now a nun, that she has chosen to be with God so she will never be alone, and her love of Alina is different from before. They return to the convent, but Alina asks Voichița that they escape together. After Voichița refuses, Alina attempts to jump down a well, but is restrained by the nuns and taken to the hospital. There, doctors restrain Alina to prevent her self-harm, after which they send her back to the convent to assist with recovery. There, the nuns read to Alina about sin. Alina begins a Black Fast, but when the Priest learns of this when Alina is not at the table, they see Alina is attempting to enter the altar to make a wish to the icon. The Priest admits the icon exists, but says entering the altar is a severe sin, and tells the nuns the Devil is in Alina and the convent. Alina remains tied down to a board with chains and towels. The nuns witness a worsening in her condition and take her back to the hospital. There, the hospital staff find Alina is dead on arrival, and observe the wounds on her wrists and ankles from the restraints. The staff tells the nuns this constitutes homicide and threatens to call the police and media. An officer investigates the convent. Seeing the board Alina was tied to, the officer interprets it as a cross. The officer also says forcible restraint leading to death is a homicide. The Priest denies criminal intent, saying the restraints were to prevent self-harm, and invoking the analogy of a parent's right to force children to take medicine, though the officer replies Alina was not a child and the Priest was not her guardian. The nuns also cite Alina's strength as mysterious, but Voichița says Alina studied martial arts. The police take the Priest and the nuns who tied up Alina away, with Voichița choosing to go with them.

The Battle of France rages in June 1940. It has turned against both the British and French. RAF pilots evacuate a small airfield in advance of German advance forces. The pilots, along with British and French military, leave just as Luftwaffe aircraft arrive and execute a heavy strafing attack. As the deserted beaches of Dunkirk are shown, where retreating British forces were overwhelmed and driven into the sea by the Wehrmacht, the BBC reports British Prime Minister Winston Churchill 's declaration that "what General Weygand called the 'Battle of France' is over. The Battle of Britain is about to begin." In neutral Switzerland, the German ambassador, Baron von Richter, proposes new peace terms to his British counterpart, Sir David Kelly, stating that with the fall of France and U.S. still determinedly isolationist continuing to fight alone is hopeless. Kelly retorts, "Don't threaten or dictate to us until you're marching up Whitehall... and even then we won't listen." Hitler delays, hoping that Britain will accept peace terms; British commanders use the delay to build up their strength, training pilots and ground controllers. The campaign to conquer Britain by air begins with the German air force launching an early morning assault on " Eagle Day ". It seeks to destroy the RAF on the ground before it has time to launch its Spitfire and Hurricane fighters. Two British radar stations at Ventnor and Dover are put out of action and a number of RAF airfields are damaged or destroyed, but losses are relatively light. A gruelling battle of attrition ensues, with airfields in Southern England under repeated attack. Tensions develop between commanding officers of RAF 11 Group, Keith Park, and 12 Group, Trafford Leigh-Mallory. Leigh-Mallory is tasked with protecting 11 Group's airfields while Park's forces are aloft engaging the enemy, but in raid after raid 12 Group aircraft are nowhere to be seen. Called to meet Dowding, Leigh-Mallory explains that the " Big Wing " tactic he has devised to assemble an air armada to attack the Germans from above takes time to form up, while Park complains that it takes too long, and the tactic is simply not working. The turning point in the Battle occurs when a squadron of German bombers lost in bad weather at night jettison their bombs, which accidentally fall on London. In retaliation to what was seen as attacks on London, the RAF attacks Berlin. An enraged Adolf Hitler publicly orders London to be razed. This takes the pressure off the RAF Fighter airfields, which had been suffering for some time before. Hermann Göring arrives in France to personally command the assault, confident that the end of the campaign nears. Their first northbound sorties skirt the RAF, which is still defending its airfields to the south, and the Germans bomb unopposed. Night attacks follow and London burns. To supplement Commonwealth forces, the RAF has begun accepting and training foreign pilots who have escaped German-occupied countries. The main difficulty is their lack of English-language skills. While on a training flight, a Free Polish Air Force squadron accidentally runs into an unescorted flight of German bombers. Ignoring commands to avoid engagement by their British training officer, they peel off and shoot down several bombers with aggressive if unorthodox tactics. Park rewards the unit by elevating it to operational status, leading Dowding to do the same for the Canadian and Czech trainees. While discussing the day's events, Park and Dowding examine the German switch to London. Given a respite, Park notes that he will be able to repair his airfields and bring his squadrons back to near full strength. Dowding observes that although enemy bombers can reach London, their fighter escort can only provide ten minutes of cover. He concludes that "turning on London could be the Germans' biggest blunder." The next German daytime raid is met by large groups of RAF fighters attacking en masse, which overwhelm the German raiders. Luftwaffe losses are so severe an incensed Göring orders German fighters remain with the bombers. Deprived of both of altitude and speed, they are easy prey for British fighters attacking from above. For the first time German losses outweigh British. The climactic air battle of 15 September 1940 arrives, with British ground control ordering every squadron into the air, leaving no reserve. Intense combat over London leaves both sides with heavy losses. The next day the RAF anxiously await a raid that never comes. Both German air and naval forces withdraw from the coast, leaving airfields abandoned and harbors empty. Göring leaves the front, accusing his commanders of betrayal. Dowding looks out over the gardens and up to the sky where the words of Winston Churchill appear onscreen: "Never in the field of human conflict was so much owed by so many to so few."