Sathya is a 1988 Indian Tamil action film directed by Suresh Krissna and produced by Kamal Haasan starring Kamal Haasan himself along with Amala. The film was remake from the 1985 Hindi film Arjun. The film is the debut directional venture for Suresh Krishna. The film completed a 150-day run and did successful box office collection. The cinematography and editing were handled by S. M. Anwar and N. R. Kittu respectively.
Sathyamurthy alias Sathya (Kamal Haasan) is an unemployed youth who does not tolerate injustice anywhere. He stays with his father Mudaliar (Bahadoor), stepmother (Vadivukkarasi) and stepsister Sudha. One day Sathya beats up a group of ruffians who are thrashing a tea vendor for not paying extortion taxes. These ruffians are the henchmen of a local goon Rangan, who works for the local MLA Mariappa (Rajesh). With this incident, Sathya's life changes as he invokes the wrath of Rangan. In retribution, Rangan and his men humiliate Sudha in public, forcing Sathya to thrash Rangan and destroy his bar. Meanwhile, Sathya falls in love with Geetha Nair (Amala Akkineni), a young Malayali woman who works as a salesperson in a cloth shop.
Soon, Sathya begins to grab public attention, as he and his friends start taking the law into their own hands, thrashing anyone who tries to break the law and harass innocents. Mariappa also gets to know of Sathya and thinks that he is working for his arch-rival Dhandapani (Kitty), who is a social reformer.
He orders that Sathya and his friends be eliminated. Mariappa's gang attack and kill one of Sathya's friends Sundar in full public view. Though Sathya tries his best, no one comes forward to give witness to the murder out of fear, because of which the murderers are released. A frustrated Sathya thrashes the murderers on their release, leading to his arrest, but is later released on bail by Dhandapani.
Soon, Sathya's family disowns him for his activities, following which he is approached by Dhandapani, who convinces him to move to his own house and work for him. With the help of Dhandapani, he manages to get Sudha married to her boyfriend (Anand), who is the local police inspector, saves the marriage of his other stepsister by paying the dowry of ₹20,000 and also ensuring that his father's employer (Kavithalaya Krishnan) treats his father with respect. Finally, Dhandapani tells Sathya to get some secret files and documents against Mariappa, which can be used to expose him in public. Risking his life, Sathya gets a hold of the files.
Now the film takes a twist as Sathya comes to known that Dhandapani is a corrupt person and double-crosser who used the evidence against Mariappa to join hands with him and contest the upcoming election in his place, and none of the evidence collected has been published anywhere. Sathya also finds out that his services are no longer needed by Dhandapani, and he is thrown out of his house.
To add to Sathya's growing frustration and anger against Dhandapani, he learns that his friend Anand was also used by Dhandapani and Mariappa to eliminate one of Mariappa's associates Seena Thana (Nassar), who is in jail, as they feel that he would turn informer against them in court.
Though Anand did the murder to get the money required to treat his sick mother and get his sister married, he does not receive the money, his mother dies and his sister elopes with somebody, forcing him to commit suicide while under custody. An enraged and betrayed Sathya barges into a political meeting where Mariappa and Dhandapani are prsent and tries to expose Dhandapani, but is forced out and thrashed by the workers of Mariappa's political party.
Undaunted, he sneaks into Dhandapani's house a few days later and takes the file containing evidence of both Mariappa's and Dhandapani's illegal activities. While on the run from Dhandapani's henchmen, he gets shot and seriously injured, but manages to survive. However, the evidence against Mariappa and Dhandapani is destroyed as Sathya used the file as a shield against the gunshots. Sathya escapes from hospital, confronts Mariappa and Dhandapani and kills them both.