A woman named Vasantha finds her husband Ranganathan murdered. A masked murderer tries to kill her too, but she escapes from him. Vasantha is left in a state of shock and becomes
mentally paralysed. A case is registered and the investigation takes place. Susi, a college student, along with her friends arrives at Vasantha's for her vacation. There live her younger paternal uncles Kamalanathan and Vimalanathan, aunt Vasantha, butler Appukutty Nair and a regular visiting
Siddha doctor Vedamurthy. During her stay, a series of murders take place at the house with every time a
cigar bit being intentionally left by the murderer . Since Vasantha is the only
eyewitness of her husband's murder, her life is in danger. Despite tight security, she is killed by the murderer, who later makes frequent calls to Susi and threatens that she will be his next target. Susi is frustrated by the incidents happening at the house and the threatening phone calls. She requests help from her colleague Baskar, who promises her to help. Baskar investigates Vimalanathan, Kamalanathan and the inmates of the house. One day, Baskar follows Kamalanathan to a strange house, where he meets a woman. She is revealed to be Kamalanathan's lover Mala, who was rescued some years back by him when she attempted suicide. Kamalanathan keeps quiet as he wants Susi to get married first, only then he would marry Mala. As a part of investigation, Baskar asks everyone in the house to stay out for a night, to lure the murderer. As expected, the murderer enters Susi's room to kill her. Baskar tries to unmask the murderer, but only sees his eyes before the murderer escapes, leaving his mask behind. Baskar finds Vimalanathan murdered at the doorstep. Kamalanathan rushes everyone to vacate the house following the celebration of Susi's birthday party. On the day of the party, the murderer tries to attack Susi, but Baskar saves her. Baskar chases the murderer, but loses track. On his way back, he sees Vedamurthy injured at a place. He rescues him and comes home. Everyone is unaware of the reason of the murder, where Baskar insists Kamalanathan in front of everyone to tell about his family which might help them to get a clue of the murders. Kamalanathan reveals that his father had an
extramarital affair with a woman, but the woman and her 10-year-old son died in a fire set by Kamalanathan's elder brother (Susi's father). Baskar theorises that the son may not have died and is actually the murderer killing the family members in vengeance; he also states that the murderer may be present amongst them as he plans accordingly knowing the circumstances of the house. Baskar places the murderer's mask on the face of each man present to verify whose eyes match with the murderer's eyes, ultimately exposing Vedamurthy, who was disguised using prosthetics, as the murderer. Baskar chases the murderer, who gets injured while trying to escape and is struggling to run. While the police shoot the murderer, he disappears in a tunnelway near the garden. Everyone finds a secret room beneath the garden which leads to the murderer's house and his corpse, realising this is how he escaped after committing each murder. Baskar later marries Susi and stays in the same house, while Kamalanathan marries Mala. == Cast ==