In a shantytown on the edges of Johannesburg, South Africa, nineteen year old Tsotsi (Presley Chweneyagae) has repressed any memory of his past, including his real name: "Tsotsi" simply means "thug" or "gangster" in the street language of the ghetto. Orphaned at an early age and compelled to claw his way to adulthood alone, Tsotsi has lived a life of extreme social and psychological deprivation. A feral being with scant regard for the feelings of others, he has hardened himself against any feelings of compassion.
Ruled only by impulse and instinct, he is fuelled by the fear he instills in others. With no name, no past and no plan for the future, he exists only in an angry present. Tsotsi heads up his own posse of social misfits, Boston, a failed teacher (Mothusi Magano), Butcher, a cold-blooded assassin (Zenzo Ngqobe) and Aap, a dim-witted heavy (Kenneth Nkosi.) One night, during an alcohol-fueled evening at a local shebeen (illicit liquor bar) Tsotsi is put under pressure by a drunken Boston to reveal something of his past; or at the very least, his real name. But Tsotsi reveals nothing. The questions evoke painful, long repressed memories that Tsotsi would prefer to keep buried. Still, Boston keeps asking. The other gang members sense a rising anger in Tsotsi and try to stop the interrogation, but Boston keeps pushing, prodding, digging. Suddenly, Tsotsi lashes out with his fists and beats Boston's face to a pulp.
The violence is brief but extreme. Tsotsi turns and flees into the night. He runs wildly, desperate to escape the pain of unwelcome images rising in his mind. By the time he stops running he has crossed from the shantytown into the more affluent suburbs of the city. He collapses under a tree. It is raining hard. A woman in a driveway is struggling to open her motorised gate with a faulty electronic remote. Tsotsi draws his gun. It's an easy opportunity for an impromptu car jacking. As he races away in the woman's silver BMW, he hears the cry of a child. There's a 3 month old baby in the back of the car. Tsotsi loses control of the vehicle and crashes to a stop on the verge of a deserted road. The car is a write-off. Tsotsi staggers from the vehicle. The baby is screaming. Tsotsi walks away. Then he turns back. The baby calms slightly when Tsotsi looks at it.
This unsettles him. He hesitates. An unfamiliar feeling stirs within him: an impulse other than his pure instinct for personal survival. Suddenly, he gathers up the infant, shoves it into a large shopping bag and heads for the shantytown on foot. Tsotsi does not reveal to anyone that he has the child. He hides it from his gang. At first he thinks he can care for it alone. Keep it in his shack. Feed it on condensed milk. But he soon realizes that he cannot cope. The baby screams constantly and his attempts to feed it fail miserably. At the community water tap, Tsotsi selects a young woman with a baby of her own and secretly follows her back to her home. Forcing his way in behind her, he makes the terrified woman breastfeed "his" baby at gunpoint. The young mother, Miriam (Terry Pheto), is only a few years older than Tsotsi. She has recently lost her husband to violent crime and lives alone with her baby, making ends meet as a seamstress. At first Miriam is very frightened by Tsotsi. But gradually she takes on the role of both mother to the baby and mentor to the desensitized young gangster. As their relationship tentatively progresses, Tsotsi is compelled to confront his own violent nature and to reveal his past.