Sigappu Rojakkal is thriller movie. Dileep (Kamal Haasan) is a successful businessman with a dark side. He preys on nubile girls and rapes and kills them. These proceedings are video-recorded and watched by his adoptive father and mentor, another deranged woman-hater who, as with Dileep, had a disillusioning experience with the female sex in his past. The old man stays holed up in a far corner of Dileep's mansion watching his son carry out what he is too infirm to do. The murdered girls are buried in Dileep's garden and a rosebush is grown above.
Dileep chances upon a undergarments salesgirl, Sarada (Sridevi), and develops an attraction for her. Sarada, a conservative woman, insists that Dileep must marry her if he wants to have his way with her. The romance proceeds, and appears to be Dileep's salvation before things begin to collapse for him. On his marriage day, Sarada stumbles upon a diary containing details of his deranged life and, and names of the girls he had killed scribbled on the walls of one of the rooms in his large house.
Sarada, meanwhile stumbles upon Dileep's father, whom Dileep had told her was retarded and was not to be disturbed, and gets the shock of her life. She somehow manages to shut him in and tries to run out but Dileep returns before she gets a chance to leave the house. Sarada puts on an agonising mask of normalcy and bides her time to escape. Dileep gets called away on business that night and she packs up her luggage and leaves the house, but is dramatically intercepted by Dileep who gets word of her flight through his watchman. A tense chase ensues, which ends in a graveyard in the dead of night, with Dileep stumbling and falling on a cross which pierces him.
Sarada immediately becomes aware of the possible trouble she would be in and attempts to leave Dileep's house. As she prepares to leave, her husband returns after killing a club waiter (Bhagyaraj), who was a witness who would have identified him as the culprit in the murder of a woman.
In the ensuing chase, Dileep is caught by the police.
He is subsequently jailed but gets mentally retarded and loses his bloodthirsty ways. He keeps repeating Sarada's name, as it is his only coherent thought, and all other memories have been erased from his mind.