In 1941, SS colonel Hans Landa interrogates French dairy farmer Perrier La Padite as to the whereabouts of the last unaccounted-for Jewish family in the area. In exchange for the Germans agreeing to leave his family alone for the rest of the war, La Padite reveals that the Dreyfus family is hidden under the floor. Landa orders SS soldiers to shoot through the floorboards. The family is killed except for Shosanna, a young woman who escapes.
Three years later, Lieutenant Aldo Raine of the First Special Service Force recruits Jewish-American soldiers to the Basterds, who spread fear among the German soldiers by killing and scalping them. The Basterds also recruit Sergeant Hugo Stiglitz, a German soldier who murdered thirteen Gestapo officers. Adolf Hitler interviews a German soldier, Private Butz, the only survivor of a Basterd attack on his squad. Raine carved the letter T into Butz's forehead with a knife so he could never hide that he voted for an avowed fascist.
Shosanna is operating a cinema in Paris under an assumed name. She meets Fredrick Zoller, a German sniper who killed 250 soldiers in a single battle; Zoller is to star in a Nazi propaganda film, Stolz der Nation (Nation's Pride). Infatuated with Shosanna, Zoller convinces Joseph Goebbels to hold the premiere of the film at her cinema. Shosanna plots with her projectionist and lover, Marcel, to kill the Nazi leaders attending the premiere by setting the cinema ablaze.
Unknown to Shosanna, British Army Lieutenant Archie Hicox is working with the Basterds to plan an attack on the same premiere. Hicox goes to a tavern with Hugo Stiglitz and Basterd Wilhelm Wicki to meet an undercover agent, the German film star Bridget von Hammersmark. Hicox gives himself away by ordering three drinks and gesturing "three" with his hand (with thumb and pinky finger down); Gestapo Major Dieter Hellstrom knows that Germans gesture "three" with the thumb and first two fingers extended. Discovered, and the Basterds open fire, killing everyone in the tavern except Wilhelm and a wounded Hammersmark. Raine arrives and negotiates with Wilhelm for Hammersmark's release, but the she kills Wilhelm when he lowers his guard. Raine learns from Hammersmark that Hitler himself will be attending the film premiere and decides to continue the mission. Later, Landa investigates the aftermath at the tavern and finds one of Hammersmark's shoes and a napkin with her signature.
At the premiere, two of the Basterds, Donny Donowitz and Omar Ulmer, join Raine in posing as Italians, hoping to fool the Germans unfamiliar with the language. However, Landa, who speaks fluent Italian, converses briefly with the Basterds before sending Donowitz and Ulmer to their seats. He takes Hammersmark to a private room, verifies that the shoe from the tavern fits her, then strangles her to death. Raine and another of his men, Smithson "The Little Man" Utivich, are taken prisoner, but Landa has Raine contact his superior with the OSS and cuts a deal: he will allow the mission to proceed in exchange for immunity and rewards.
During the screening, Zoller slips away to the projection room to see Shosanna. After she rejects his advances, he becomes aggressive. She pretends to acquiesce, then pulls a pistol from her bag and shoots him. Zoller, mortally wounded, raises his pistol and shoots her before they both die. As Stolz der Nation reaches its climax, spliced-in footage of Shosanna tells the audience that they are about to be killed by a Jew. Marcel, having locked the doors of the cinema, ignites a pile of flammable nitrate film behind the screen as Shosanna's image laughs. Ulmer and Donowitz break into the box containing Hitler and Goebbels, killing them, then fire their submachine guns into the crowd until the bombs go off, killing everyone in the theater. Landa and his radio operator drive Raine and Utivich into Allied territory, where they surrender. Raine shoots the radio operator and carves a swastika into Landa's forehead.
Output: Why do the Basterds scalp the German soldiers they have killed?