The movie starts off with archive black-and-white footage of the Nazi's atrocities on the Jews across Europe. The focus shifts to West Belarus, where Nazi SS soldiers, under the command of Bernicki, the Belarussian Police Captain, are busy "sanitizing" a village, killing half the people and abducting the rest. Zus Bielski (Liev Schreiber) and his brother, Asael (Jamie Bell), watch helplessly from the forest. Once the Germans have left, they run to the village and are devastated to find their father dead. They go to their house and find their youngest brother, Aron (George MacKay), cowering under the floorboards in the closet. They take him with them to the forest.
In the Lipiczanska Forest, Zus tells a weeping Asael to get a hold of himself. As they sleep, their eldest brother, Tuvia Bielski (Daniel Craig), walks up to them and wakes them up. He first admonishes Asael for not being alert, then embraces him and Aron emotionally. Zus and Tuvia have a rather curt reunion. As they walk into the forest, Zus tells Tuvia that his wife and child are hiding in a village. At night, they discuss their options. The police are after them, however they are safe in the woods. They talk about Bernicki. A friend, Koscik has a gun which they can borrow. Next morning, Aron stumbles across some other Jewish refugees in the forest. He brings them back to his brothers. One of them is a young child, mortally wounded. Unfortunately, they can't save her. As her parents grieve, Zus tells Tuvia that they can't support these people. Tuvia says he'll ask Koscik for food and his pistol.
In the nearby village, Konstanty 'Koscik' Kozlowski, their friend and a secret Jew-sympathizer, lets Tuvia inside and gives him food, drink and his pistol, with only 4 bullets. Seeing a police car coming towards the house, Koscik hides Tuvia in the barn, along with some other Jews. It's Bernicki and his sons, who Koscik welcomes warmly. Bernicki talks about his Jew-hunting exploits. Bernicki talks about having killed the Bielskis' father and is now after the sons. He tells Koscik to keep his eyes open and leaves. After they're gone, Koscik gives Tuvia food and drink and asks him to take the Jews from his barn. Tuvia confirms that Bernicki and his sons were responsible for his parent's deaths. He then takes the other Jews and goes into the forest.
As they walk into the forest, one of the Jews, an elderly man named Shamon Haretz, Tuvia's old school-teacher, talks to him about his experiences. Tuvia brushes him off. At the campsite, the food is being passed around, with each person taking a small morsel so the others can have some. Zus is upset that Tuvia brought more mouths to feed. Tuvia tells him that it was Bernicki who killed their parents. That night, he goes to Bernicki's house, where he is having dinner with his wife and two sons. Tuvia bursts inside and holds them at gunpoint. He asks them if he knows who he is and why he's there. Terrified, Bernicki says he did as ordered. Tuvia orders him to his knees. Bernicki's sons jump up to their father's aid, but Tuvia shoots them dead. He then shoots Bernicki dead. Bernicki's hysterical wife pleads with Tuvia to kill her as well. Leaving her alive and grief-stricken, he leaves.
The next morning, Tuvia tells Zus he killed Bernicki and his sons. They decide to move deeper into the woods. Tuvia brings over more Jews, much to Zus' displeasure. One of them is Isaac Malbin (Mark Feuerstein). The refugees start building makeshift houses in the woods. After almost hitting Zus with a log, Isaac confesses that he's an intellectual, not a carpenter. A refugee introduces Tuvia to his "forest wife". Tuvia congratulates them, a bit unsurely. Just then, two men burst into the scene, one of them holding a rifle, while the other demands food. Zus gets confrontational, despite being unarmed. He dares the man to shoot him, a Jew. When the two hear that they are Jews, they say they're Peretz and Jacov, from Zus' village. Almost all the people in the village are dead, including Zus' wife and child. Zus is devastated and grieves for his wife and child. He starts to hit his head against a tree trunk, but Tuvia grabs him and holds him, while he cries.
Later, Peretz asks which Otriad (armed brigade) they are. Asael replies the "Bielski Otriad". Peretz tells them that there is a Russian Otriad, which sabotages railways and kills Germans. Zus tells them, if they want to kill Germans, to follow him. Tuvia tries to dissuade him, but he's resolute. Reluctantly, Tuvia goes with the small group. They attack a town that supported the Nazis, killing a few people. They then attack a German motorcyclist, killing him and stripping him of his weapons. A German jeep comes down the road. The Bielskis hide along the road and wait. The jeep stops nearby seeing the fallen motorcycle. One of the Germans goes to the side of the road to relieve himself and does so right on Zus. Enraged, Zus stabs him to death, while the others attack the jeep. One tries to run, but gets gunned down by Asael. Zus picks up the machine gun of the guy he killed and unloads it on the jeep's occupants, killing them all. As they scour the jeep for weapons and food, a German truck comes down the road. Jacov is shot dead, while Peretz is injured. Asael takes to his heels, chased by German soldiers, while Zus and Tuvia take cover, watching helplessly as their brother sprints away, dodging German fire. They manage to shoot out the truck's spotlight, but find themselves outgunned. They have no choice but to retreat, leaving Asael to his fate.
At the camp, Tuvia is furious at Zus. Food is dangerously low. Peretz is dead from his injuries. Shamon is upset that they didn't bring back any food. He quotes from the Talmud, saying that if they save a life, they must take responsibility for it. Suddenly, an armed man walks into the camp. Zus is irate that the man keeping watch didn't see him. He punches the man and says he should be killed, but Tuvia will have none of it. He's still angry at Zus and holds him responsible for Asael's fate. The man, Ben Zion Gulkowitz, tells Tuvia that he's from a village, where everyone was murdered, but he managed to escape. People start to cry and argue about their predicament. Tuvia yells out that they all have to live together or they'll all go against each other. He tells Zus that they can't go killing Germans and can't afford to lose more people. They will go to villages for food and take only what is offered to them. Their revenge is to live. They may be hunted like animals, but they won't become animals. If they should die, then it'll be as human beings.
Tuvia, Zus and Ben Zion go to Koscik's house and find his body hanging from his barn. He's been beaten badly and has a sign "Jew Lover" hung around his neck. They dig a grave for him. Koscik's wife shows them a secret cellar under a haystack. They find Asael hiding there. They have a happy reunion. They find rifles hidden in the barn. They also find two Jewish ladies in the cellar. The older one is Bella and the younger one is Chaya. Zus is a bit taken in by Bella. At the campsite, Shamon and Isaac engage in an intellectual debate, as they work. Tuvia notices that Asael's shy interest in Chaya and encourages him to talk to her. He tells Asael to accompany Zus on the next expedition and to ensure that no one is killed.
Zus, Asael and Ben Zion waylay a milkman, Kissely, on the road. They ask for his milk. He pleads that the Germans will kill him if he doesn't meet his quota. They only take half of his milk, but Zus also takes the man's coat. At the campsite, they are welcomed with glee. One of the men, Arkady Lubczanski, takes an interest in Chaya. He tries to force her to become his forest wife, but she declines politely. Ben Zion tells Tuvia that new refugees have arrived from Novogroduk. Bad news is, Tuvia's wife is dead. Though saddened, Tuvia maintains his composure. Bella goes to Zus and asks if she can be his forest wife, which he willingly accepts.
Aron sees some Belarussian policemen and German soldiers, being led to the campsite by Kissely. He runs back to the camp to report. Tuvia orders that the people evacuate the camp immediately, while a few people remain behind to stave off the attackers. Once the refugees are relatively safe, Tuvia and the fighters take cover behind trees, overlooking a small rivulet. When the policemen and soldiers come to the rivulet, the partisans fire at them, injuring a few. The soldiers and Kissely take cover behind trees as well. They yell at each other. The leader of the soldiers tells them to hand over the Bielskis and the rest can go free. Tuvia asks the leader why he, a Belarussian, works for the Germans. Kissely yells out to survive, but Zus shoots him in the arm. The partisans shoot at the attackers, forcing them to retreat. When they're gone, Zus angrily tells Tuvia that he should have killed the milkman before and that it's his fault that they now have to relocate. The refugees walk past a field into another section of the woods.
As Tuvia and Zus survey the woods, they are confronted by a group of Russian partisans. Tuvia tells them that they're from the Bielski Otriad and they want to see their commander. They are taken to the Russian partisans' camp, where they meet Viktor Panchenko, leader of the October Otriad. Panchenko accuses them of stealing from villages loyal to them. Tuvia responds that when they (October Otriad) take food, it is support, but when the Bielskis do it, it is stealing. He tells Panchenko that they fight a common enemy. Though he doesn't believe Jews can fight, Panchenko tells them to send him their best fighters.
Back at the new campsite, the refugees are doing their best to set up a camp, before winter sets in. A new bunch of refugees is being escorted inside. One of them, Yitzchak Shulman, tells Tuvia that he is from the Baranovichi ghetto. The Germans will kill everyone if anyone is found missing. Chaya's parents are also inside the ghetto. She pleads with Asael to do something to get them out. Tuvia decides to go to the ghetto to save all the Jews inside from imminent massacre. Zus is skeptical. They argue for a while, culminating in a fistfight, which ends with Tuvia just about restraining himself from bashing Zus' head in with a rock. Tuvia walks away. Zus takes Ben Zion and some other fighters to the Russian partisan camp. Asael stays behind.
Tuvia and Asael sneak into the Baranovichi ghetto and talk to the elders there, regarding their escape. The elders are incredulous that the Germans would kill all of them just like that. Tuvia promises to keep all of them safe in the woods. One by one, all the people in the ghetto agree to go to the woods, including Lilka Ticktin (Alexa Davalos). That night, under cover of darkness, Tuvia and Asael get the Jews out of the ghetto. When they reach the camp, they are asked to surrender their valuables, which can be traded for food and weapons. Chaya has a happy reunion with her parents. Isaac and Shamon ask about people who know useful trades, like carpentry. Tuvia gets on his horse and gives a speech. He says that everyone must work, women will learn to fight alongside men, pregnancies are forbidden. They will rebuild their lives.
Bella encourages Asael to propose to Chaya. He does so awkwardly and she readily accepts. They are married just as winter starts. As this happens, the October Otriad, assisted by Zus and his fighters, attacks a German convoy, killing everyone on board. Panchenko is impressed by Zus' ruthlessness.
Soon, winter sets in. Food supplies are low and people are cold and starving. Tuvia, left with no other choice, shoots his horse dead, so the people can eat. At suppertime, the lines get unruly as horse meat (though considered non-kosher) is served. Tuvia enters a cabin to warm himself and sees Lilka inside. She's on her way out for her first food mission. He gives her his coat and his pistol, just in case. Arkady comes in and pokes fun at Tuvia. A woman informs Tuvia about sickness that is spreading through the colony. Lilka, having got a sack of food, encounters a wolf on the way back. It attacks her, but she manages to kill it. She takes the wolf and the sack back to the camp. At the camp, the sickness is found to be typhus. The Russian partisans have ampicillin, but won't part with it.
Tuvia goes to the Russian partisan camp to ask for ampicillin. Panchenko is strategising with Zus about a transmitter at Police HQ, which has caused them much trouble. That transmitter has to be silenced. Tuvia comes to Panchenko and asks for ampicillin. Panchenko refuses, but Tuvia insists. Zus calms the situation down, by suggesting they hit a police station and take out the transmitter there. Outside the police station, Zus sees that Tuvia's also been affected by typhus. He tells him to wait in the car, while he, Ben Zion and another man attack the station. The attack is a success - the transmitter is destroyed and the ampicillin is stolen - but Ben Zion and the other man die, while Zus is wounded. He and Tuvia drive back. Tuvia asks Zus to come back to the camp, but Zus declines.
As the funerals for Ben Zion and the other man are underway, Tuvia sits in his cabin, coughing uncontrollably. The next day, Arkady demands more food from Chaya, during lunchtime. He tries to take more, but Asael pushes him away. They draw their knives and they are restrained by the others. Tuvia breaks it up and tells them, as punishment, Arkady and Asael get only half rations. He walks away, coughing. Asael confronts him regarding rumours about him being power-hungry and corrupt, and that he is no longer fit to lead them. The next day, during lunchtime, as Tuvia sits coughing badly in his cabin, Arkady has pretty much taken over. He and his cronies have beaten up Asael and have taken the lion's share of food rations for themselves. Tuvia, hearing all this, steels himself and gets up. He walks outside and sees Arkady and his cronies sitting at a table, being served by Chaya. Tuvia sees Asael's bruised face and confronts Arkady. Arkady tells him it's the new policy that fighters get better food. Tuvia is no longer the leader. As Arkady laughs derisively, Tuvia shoots him dead. He orders the cronies to obey him. Anyone who wants to leave can do so. No one argues and he's the leader again.
He gets better under Lilka's care. Soon, the sun comes out and it's springtime. The ice melts and spirits are lifted considerably. One of the women, Tamara, reveals to Lilka that she's pregnant and the baby could come anytime soon. She is terrified of what Tuvia would do when he finds out. Lilka comforts her, saying he'll understand. Tamara tells her that she was raped by a German soldier. When the baby is born, Tuvia hears the cries and finds it in a cabin with Lilka and other women. He is angry and confronts Lilka about it. He wants Tamara and the father to leave, but Lilka tells him Tamara was raped. She reminds him of his own words - to not become animals. He agrees. Happily, she kisses him. They share a passionate kiss.
Aron sees a German convoy passing by. Back at the camp, the lone surviving soldier of a partisan raid is dragged into camp. The terrified German is paraded before the partisans. They've also found a pouch containing information about an attack on the camp in two days. The German pleads for his life, saying he has a wife and kids. That just enrages the partisans even more, as they've lost everything. They proceed to beat the German to death. While Shamon and Isaac try to stop them, Tuvia watches indifferently.
The next day, Panchenko tells Zus that they're leaving the forest as the Germans are going to attack. The Bielski partisans will be sacrificed to the Russian partisans can escape. Zus is upset and tries to protest, but Panchenko says that if he tries to desert, he'll be shot.
At the Bielski camp, they notice a German scout plane overhead. Tuvia orders everyone to evacuate the camp. Just as the people start to evacuate the camp, a couple of Luftwaffe planes fly towards them. Tuvia yells for everyone to take cover. The planes dive-bomb the camp, killing many. A bomb hits close to Tuvia, leaving him dazed and blinded for a while. Asael orders the fighters to arms, as German soldiers are expected to attack soon. The rest of the people are to evacuate. Tuvia is to lead the refugees away, while Asael stays back to fight. The Germans attack, killing all the fighters, except Asael, who manages to escape barely. However, they managed to stave off the Germans long enough for the refugees to make good their escape.
Tuvia and the refugees come up on a large marshland. Unsure of whether Asael is alive or not, Tuvia finds himself unable to decide whether to stay or go. Asael runs up and tells them that the troops are behind them. They should cross the marsh if they are to survive. Gathering rope and everyone's belt, they make a long enough chain, so they can go through the marsh. They start to wade through the muddy water warily. Soon, they make it to the other side of the woods. Shamon, however, is in bad shape. He thanks Tuvia for having saved them and thanks God. He dies shortly after.
Suddenly, they find themselves being attacked by a tank and a company of German troops. In the ensuing battle, a number of partisans are killed. Tuvia takes Isaac and they flank around to the rear of the attackers. They kill a machine gun squad and commandeer the machine gun, opening fire on the troops, killing many. However, they are discovered and the tank starts to slowly turn its turret towards them, as the troops fire at them. As the turret stops, they abandon the machine gun and take cover behind the trees, as the Germans fire incessantly at them. Isaac grabs hold of a potato-masher grenade, arms it, looks one last time at Tuvia and runs towards the tank. However, he doesn't get more than twenty yards, as he's shot dead by the troops. The grenade blows up near him. Just as things look really bad for Tuvia, the Germans are ambushed from behind by Zus' men. After killing many Germans, Zus jumps on the tank, killing the gunner and throwing in a grenade. The tank implodes. The partisans complete cleaning up the remaining Germans. Tuvia comes out of cover and orders everyone into the forest. They strip the dead of their weapons. Zus and Bella reunite. Tuvia and Zus, after a long wordless encounter, embrace each other emotionally, as Asael watches with a smile. They all walk into the woods.
We are informed that they lived in the forest for two years. Their number grew to 1200. Asael died in action and never saw his and Chaya's child. Zus and Tuvia emigrated to New York and started a trucking business. Tuvia and Lilka remained married for the rest of their lives. The Bielskis never sought recognition for their actions.
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