Dalapathi 1991 || Telugu movie trailer || ManiRatnam | Rajnikanth | Mammootty

14-year-old Kalyani delivers a boy in seclusion, fearing societal backlash and incapacity. She abandons him, heavy-hearted, placing him inside a moving goods train, which a slum dweller finds. The slum procures him as their common child, naming him Surya and they collectively raise him honest. He grows up, intolerant of injustice especially to the poor, though he wonders why his biological mother had impetuously abandoned him. A yellow shawl was the only identity he had of his mother, which she had placed him in when casting him away.

Devaraj, a powerful don who is kind yet feared by most in the society, also fights injustice, but by violent means. Ramana, an auxiliary of Deva's, whose abusive demeanour led Surya to attack him, succumbs to his death. Surya gets apprehended for this. An exasperated Deva soon perceives Ramana's felony, realises Surya's cause was genuine and bails him out. Thus, Surya and Deva get to understand each other as both share similar social ideologies despite getting off on the wrong foot. Deva declares Surya his "Thalapathi" (commander) and best friend.

Arjun, the city's new district collector, wants to end violence by lawful means. He is the second son of Kalyani, now a doctor. After the abandonment of her firstborn, she wed a man who accepted her, despite knowing her past. Never did Kalyani let Arjun know the ordeal she faced as a teen, but is constantly grieved by thoughts of her long-lost first child. Meanwhile, Surya gets wooed by a Brahmin girl, Subbalakshmi who is smitten by his transparent nature, restraining crimes.

Surya's appraisal to Deva leads the people in the locality to pay utmost respect to both. Both of them continue objecting to societal incongruencies, which other dons, like Kalivardhan, incite through moles in governance. While Deva leads Surya to help curb those unlawful discrepancies, Subbalakshmi initially despises Surya's use of violence and tries to persuade him against it. Deva tries to get an alliance between Subbalakshmi and Surya, but her Orthodox father opposes her marriage to Surya, an orphan. Her marriage is subsequently arranged with Arjun.

Arjun turns to target Deva and Surya as they inflict violence, in the name of fighting organised crime. His attempts to chain them are futile. Meanwhile, Padma, Ramana's widow, makes Surya feel guilty for the sufferings he brought her by killing Ramana. Deva, understanding the pain a widow and single mother bears, shelters them. Padma, however, confesses that she is constantly troubled by the men surrounding her with dishonourable intentions, who concoct reasons to make advances towards her. Deva, considering Padma and her daughter's safety and Surya's future, requests both of them to accept each other. A guilt-ridden Surya marries Padma, and wins her child's affection eventually.

Later, at a medical camp, Kalyani meets Padma and her daughter along with the same shawl in which she wrapped Surya. Kalyani's husband, too, indicates that Surya was actually Kalyani's long lost son during a suspect identification. He secretly meets Surya and reveals the truth of his origin to him. Surya asks his stepfather to promise not to let his mother know of him as it would pain her to know that her son has grown to be a vigilante. Kalyani eventually finds Surya and meets him. Surya vows that he will not harm Arjun for her sake.

The long-standing feud between Deva and Kalivardhan, who is Deva's main rival, in due course of time, makes Surya admit the truth about his family when Deva doubts Surya's intentions after learning of his secret meeting with his stepfather and mother. Deva is pleased to know that, despite knowing Arjun was his half-brother, Surya still preferred to side with him and support him during unforeseen situations, thus valuing their friendship over family. As an outcome of this, Deva decides to surrender.

Deva and Surya meet Arjun, who now knows who Surya is through his mother. Suddenly, Kalivardhan's men open fire, and Deva is killed in the shootout. Filled with anger and vengance on the death of his best friend, Surya murders Kalivardhan's henchmen and proceeds to murder Kalivardhan. He surrenders to the police, but is released due to lack of evidence. Arjun is later transferred and relocates to another city with Subbalakshmi, while Kalyani prefers staying with Surya.