Whistle

Swetha, a college student, is found murdered in her car on a highway, starting the chilling mystery. No one has heard from her since, leaving the group of friends to wonder what happened. The unresolved case plants a seed of fear on the campus as whispers of the Naga legend grow louder.

The campus is abuzz with stories of a killer called Naga, though many dismiss it as a hoax. A fire in 1987 devastates the old laboratory behind the college, killing all the occupants. Since then, the abandoned lab is whispered to be Naga's private residence.

Maya and Anjali, part of the college's media circle, challenge the legend and venture to the abandoned place at night. There they are confronted by Vinod, who uses the moment to prank them and heighten everyone's nerves. The encounter hints that people around them may be playing tricks, but it also foreshadows real danger.

Meera is attacked in her room by an unseen killer wearing Naga's menace. Anjali hears Meera moaning and, thinking it is a drug episode, refuses to switch on the light. When she returns later, she finds Meera dead, revealing Meera's troubled life and descent into drugs.

Jeeva brings an old magazine about the laboratory fire, and the trio realizes Professor Panner may have survived. They break into Panner's room to investigate and hide in a secret room behind a shelf when someone nears. They glimpse a Naga outfit—a mask, cloak, and axe—before Panner himself confronts them and warns them.

Vinod is found dead, having been hanged, and the crime is initially treated as one of his pranks. Anjali suspects that Naga could be behind it, accelerating the dread that the killer is among them. The realization deepens as the danger becomes more personal.

Jeeva publicly attacks Panner in the college magazine, triggering tension within the group. The principal suspends Jeeva for a week as suspicions rise around the others. A startling truth emerges about Anjali: she has a police record from school, complicating trust within the circle.

During school days, the friends–except Maya and Jeeva–torment a junior named Saravathy during Whistle Day by staging a nude photo prank. Embarrassed, Saravathy hangs herself, and the six friends are punished with six months' consequences. The weight of that act resurfaces as the group faces the current killings.

Barath is locked in the men's toilet during the annual day function and later disappears, only to be found dead. Soon Professor Panner is murdered as well, deepening the fear. Maya and Anjali hurry to Jeeva's home and discover Panner's dead body there, intensifying the sense that the killer may be among them.

Maya and Anjali become convinced that Jeeva is the killer and warn Sharmi, who works at the college radio. Sharmi claims she sees Jeeva at the radio station, but before they can intervene, Naga strikes and kills Sharmi. The trio is left terrified and more distrustful of their own group.

Jeeva reveals the shocking twist: there are two Nagas, Maya and Baji, who have been carrying out the murders. Maya explains that Saravathy is her younger sister, and their parents died after hearing of Saravathy's death. Baji, their loyal servant turned ally, helped them, and they joined the college to seek vengeance, even killing Panner when he uncovered the truth.

Baji and Maya attempt to bury Anjali alive in a re-enactment of Nagamma's crime, but Jeeva arrives in time to rescue her. A violent confrontation ensues, Baji is killed, and Syed fatally shoots Maya to stop the rampage. The killer duo's plan collapses as order is restored, at least for now.

Years later, a new batch of students studies the Naga legend at the college. While some remain skeptical, Maya revisits the site and admits she still believes in Naga. She ominously hints that she will continue the killings against non-believers.