The film takes place at an isolated university in the middle of the Coimbatore forest. The hostels for students are nearby and the women's hostel, D Block, is in the middle of the forest.

Swathi, a first year class leader, sees something disturbing and informs her friends. However, they pacify her and believe that she had imagined it. Later, when she visits the hostel terrace, she is dragged away by an unknown figure. In the morning, she is found dead.

The university administration cover up the cause of her death as a tiger attack, and the principal bribes the police. Meanwhile, Maya, a senior student, meets with Arul and his friends and shows them a drawing of her friend Poornima. Poornima's picture was drawn 4 years ago, but exactly matches Swathi's drawing. Maya suggests that there is someone behind the death, but Arul and his friends refuses to accept it.

One night, Arul and his friends sneak into D Block to meet with Arul's girlfriend, Shruti, on her birthday. They see a terrifying figure on the roof of D Block and become scared. When they attempt to inform the college administration, the principal and warden refuse to believe them.

Arul, his friends and Maya decide to investigate the mystery themselves. They discover that eight other female students had died in the same way as Swathi. One of the dead girls was the daughter of a security guard who had previously worked at the university. Arul and his friend go to see the guard, and find the girl is alive, but mentally ill. The watchman tells them that the deaths in the university were not caused by a tiger, but by something else.

The friends approach a cafeteria worker at the university to learn more about the past. The cafeteria worker tells them that a person named Kaali had peeked into girls washroom while a girl is showering and was brutally hit by college boys and was sent to police station. The inspector while getting his details recognised he is the same Kaali, who had suffered from mental illness since childhood, had been involved in the construction of D Block. As a child, Kali had kidnapped and killed two girls. Three other girls were also later abducted and two of them were killed. The surviving girl had identified Kali as the killer, and the police had arrested Kali and sent him to a rehabilitation center. Later, Kali ran away from the rehabilitation center, and became involved in the construction of D Block as a labourer. One day, Kali was caught sneaking into the women's bathroom by several students. The students beat him up before handing him over to the police, but Kali manages to escape. From then, he begins to kidnap and kill girls at the university.

Arul, his friends and Maya find Kali's entry point into the hostel. They investigate the forest, but cannot find anything, and Arul turns to old issues of the college magazine for clues. Later, Arul sees some photos taken by his friend at the forest and realises that Kali had been standing behind them, and that his next target is Maya. He tries to warn Maya but fails, and he sees Kali pushing Maya from the D Block terrace. Maya's death is ruled as suicide.

Arul tells his friends and Shruti that five of Kali's eight victims had been bharatanatyam dancers. At his insistence, Shruti make interviews all of the classical dancers in the hostel, and finds out that one of the girls has recently seen him. Arul and his friends believe that she is Kali's next target. That night, Arul and his friends enter the D Block to protect the dancer with the help of their friend, Ria. However, when they find out that the girl has a short hair, Arul realises that Kali doesn't target classical dancers, but girls with long hair. At the same time, they find out that Kali has kidnapped Shruti.

Arul and his friends find Shruti in the forest and bring her back to the hostel. They inform the police and wait for them to arrive, but an enraged Kali returns to the hostel and tries to kidnap Shruti and Ria. Arul, his friends and their seniors struggle to stop him. All of the girls in D Block join forces, and Ria plots an idea to weaken Kali and trample him to death.