In 17th-century South Malabar, Thevan and his friend Koran get lost in a forest. That night, Koran is seduced and killed by a yakshi. Thevan flees and finds a ruined mansion. Its cook brings him to the aged lord, Kodumon Potti, who asks him to sing. Impressed, Potti insists that Thevan stay in the mansion for the rest of his life.
The cook tells Thevan that Potti descends from a sorcerer, Chudalan Potti, who was given a chathan, a goblin spirit, by the goddess Varahi. The sorcerer tortured the chathan, which took revenge and killed his family. Kodumon Potti is said to have defeated it and chained it in the attic. Thevan learns that the previous singer who stayed there went mad and was buried in the backyard.
Thevan tries to leave, but a spell makes him sick whenever he reaches the gate. He starts losing his memory, unable to remember his own name or how long he has been there. The cook reveals that the Potti they serve is actually the chathan in disguise. It had imprisoned the real Potti in the attic until he died. The only way to defeat it is to put out an ever-burning lamp in a secret chamber.
The cook steals the chamber's key and blows out the lamp, weakening the chathan. He and Thevan fight it and set it on fire. The cook, revealed as Potti's illegitimate son, tries to put on the chathan's ring to control it, but Thevan stops him, believing its power will corrupt anyone. They struggle as the burning mansion collapses.
Later, "Thevan" walks away from the ruins and is attacked by the cook, who realises that this is the chathan in Thevan's body. The cook flees and is shot by a Portuguese soldier. As Portuguese troops march towards the mansion, the chathan, still in Thevan's form and wearing the ring, walks away.
