The film weaves two parallel lives into a single, morally tangled tapestry. At the center are Magadevan, Magadevan, a Chennai cab driver who also moonlights as a thug for a corrupt politician, and Muniraj, Muniraj, a compassionate Good Samaritan and organic farmer living in a village near Erode who lives by the teachings of Swami Vivekananda and a deep respect for Tamil literature. The movie makes it clear that Maga is an atheist while Muni practices yoga and Hindu philosophy, setting up a nuanced contrast between their beliefs and choices.
Maga cherishes his wife, Viji, and their five-year-old son Prabha, and he clings to a fragile dream of turning away from crime. Muni, by contrast, is content with the love of his mother, desires to remain a lifelong bachelor as a path to knowledge, and hopes to share wisdom with his students. Deepa, a journalism student and the daughter of a local landlord named Jayaraman, looks up to the soft-spoken Muni, adding a layer of affection and social tension to their world.
Trouble erupts when Guru Narayanan, a rival of Muthuraj, schemes to pin Maga in an earlier murder. To shield himself, Muthuraj colludes with the police, casting Maga as the culprit. At the same time, Jayaraman disapproves of his daughter’s association with a man from a lower caste and plots to eliminate Muni, setting off a collision of loyalties that rips apart both families.
Jayaraman hatches a deadly plan to kill Muni with a snakebite on his farm, but Deepa steps in and helps him reach a hospital, saving his life. Meanwhile, Maga is branded the murderer of Surya Narayanan, Guru Narayanan’s brother, and goes on the run with his family. Desperate to start anew, Maga asks Muthuraj to pay him his remaining money so he can vanish toward Vizag, but the truth behind their tangle slowly comes apart as Muthuraj betrays Maga by leaking his location to the police. A furious pursuit follows, and Maga is shot while fleeing, then manages to board a goods train and escape.
The chase winds through hospitals and police stations as officers track Maga by his mobile signal. Maga reaches out to Muthuraj again, asking him to arrange a meeting with Jayaraman in Erode to secure money for a new life. Meanwhile, the authorities corner Muni at a hospital, arresting him in a case of mistaken identity—believing him to be Maga.
Maga finally reaches Jayaraman’s house, where a drunken Jayaraman, overwhelmed by fear and prejudice, mistakes Maga for Muni and tries to strike him. Maga defends himself and kills Jayaraman to survive, a brutal moment that crystallizes the double-edged nature of his world. His friends uncover the truth about Muthuraj and expose the betrayal, leaving Maga to grapple with the sense that his closest ally may have destroyed his life.
In a twist of fate, Muni is handed over to Guru Narayanan by a corrupt inspector named Devaraj, and the latter’s henchmen assault Muni, believing him to be Maga. Muni is grievously injured and admitted to the hospital, while Viji and her son are arrested, and Viji, convinced that Maga is dead, jumps into a well to escape a life of danger. When Maga learns what has happened to Muni, he hurries to the hospital and discovers that they are twin brothers, separated in childhood after their mother Deivanai, whose mental illness drove her away, left them on an empty platform.
A surge of anger drives Maga to seek vengeance against the people who wronged them. He returns to Muthuraj’s fortress and eliminates the corrupt nexus—Muthuraj, Guru Narayanan, and Devaraj—before he himself is wounded by the police. He ends up in the same hospital as Muni, but Muni dies in the ward, his peaceful path cut short. Months later, Maga arrives in Muni’s village, burdened by guilt, and chooses to follow in his brother’s footsteps—turning toward literature and a life of quiet dignity. Prabha’s future is rescued and protected by Deepa and Deivanai, and as a final note of reclamation, Maga declares his name as he walks into a life that merges Magadevan with Muniraj: Magamuni.
