Plot

While hunting in the jungle, one day, forest officer Vijay (Sunil Dutt) saves the life of a young man from the sudden attack of a wild hawk. There and then Vijay realizes that he have just save the life of a miraculous snake Naag (Jeetendra) (tha cobra reveals its true form to Vijay, when Vijay tells him that he is writing a book on cobras who can take the form of human beings) who have the powers to take the form of a human (only 1 snake out of millions can survive for 100 yrs before they can have this power) and who have been dating his beloved; also a miraculous female snake Naagin (Reena Roy). Naag also reveals the existence of a precious gem under the possession of the miraculous snakes. Naag asks Vijay to meet him the next night (new moon night), when he will be meeting the Naagin.

Vijay sends this news to his five friends (Raj (Feroz Khan), Suraj (Sanjay Khan), Uday (Kabir Bedi), Rajesh (Vinod Mehra) & Kiran (Anil Dhawan)). The friends refuse to believe Vijay, but they are astonished to see it live at the location which Naag had given Vijay. The friends immediately shoot the male snake to death in order to steal the precious gem. But the Naagin covers the precious gem and escapes. This was her honeymoon night with the Naag. The Naagin comes back to meet the dying Naag and sees the images of his 5 killers in his eyes. Vijay's Fiancé Sunita (Rekha). Raj's Fiancé Rajkumari (Mumtaz). Uday's Wife Sheela (Neelam Mehra). Rajesh's Fiancé Rita (Yogita Bali) & Rajesh's Mother (Sulochana Latkar). Suraj's Daughter Anu (Master Bittoo) & Suraj's Sister Meena (Heena Kausar) + Meena's Husband (Roopesh Kumar).

Enraged at the brutal killing of her beloved; the female snake begins to take revenge on the six friends, killing them one by one by taking the form of humans. She first strikes Kiran, who fired the bullet. She lures Kiran in the jungle, while he was sleeping in his cabin. Kiran recognizes her as the Naagin, but she says that she is a Saperi, who was in control by the Naag, and Kiran has saved her. She offers herself to Kiran, which he accepts. But once inside, the Naagin bites Kiran and kills him with his poison.

Rajesh's mother & Rita hire a Hukka Bhopali Sapera (Jagdeep) to protect Rajesh from the Naagin. He catches a snake in Rajesh's room, which looks like the Naagin. The real Naagin takes the shape of Rita and lures him out of the house and into the hotel, with a promise of sex. The Naagin is about to bite Rajesh, when Rajesh's friends (Aruna Irani) arrive and insist that they take part in a dance competition. The real Rita arrives and meets Rajesh's mom, who calls Vijay. As they track down Rajesh, the Naagin lures Rajesh away from the dance and reveals her true form and bites him.

Now the only one who can save the 4 friends is a sage (Premnath). The sage gives the 4 survivors an amulet to keep on their persons at all times to repel the Naagin. But Uday doesn't believe in this and throws the amulet away. The sage proves to Uday that his amulet works when he brings a live snake who only goes after Uday till he picks the amulet.

Uday's car gets punctured in the middle of the jungle. As he is changing car tire, he saves a village belle (Prema Narayan) from being raped by goons. Uday takes her home and learns that the goon had brought her from the village on the pretext of marriage, but wanted to turn her into a prostitute. The village girl tries to seduce Uday, and notices the amulet in his neck. She asks for brandy (as she got wet) and proceeds to poison it (as she is the Naagin). Uday is about to drink it, only to be saved by Vijay, who reveals to Uday that the village belle is the Naagin. Naagin approaches the sage and warns him not to protect the murderers of her Naag.

Now Naagin convinces a good Samaritan (Ranjeet) that Uday is her husband and has forsaken her for a mistress. The man goes to fight Uday, and wont listen when Uday insists that the village belle is a Naagin. The village belle convinces the man that Uday is under evil magic curse due to the amulet. The man fight Uday and removes the amulet and that very second the Naagin bites Uday, striking him dead.

Now Raj and the sage corners the Naagin in the jungle and capture her. But the sage refuses to sell the Naagin to the survivors as they want to kill her, he says that sages pray to the Naagins. But the survivors strike a deal with Bhopali Sapera and buy the Naagin for Rs 20K (the sage had left the Naagin in his care). Raj shoots the Naagin and burns its body. They think the curse is over. Meanwhile Meena wants to divorce her husband as he objects to her spending time in bars and discotheques. The Naagin (who was alive) disguises herself as Meena and enters Suraj's house. She wraps herself around Anu and forces Suraj to remove the amulet and throw it away. The next moment, she strikes Suraj dead.

Raj goes after the Naagin and Rajesh follows him. Raj attacks Rajesh as he thinks Rajesh wants all 5 friends to be eliminated, so he can pocket the shares of all of his 5 friends. Rajesh proves that his heart is pure when he shows Raj a will in which everything has been left to their families. Raj is visited by his fiance Rajkumari and he suspects her to be the Naagin in disguise. Raj shoots at Rajkumari, but Rajesh arrive on time and pull Rajkumari away. The Naagin enters the house, traps Rajkumari and renders her unconscious. She disguises herself as Rajkumari, seduces Raj and convinces him to remove his amulet as a sign of God, around which they take wedding vows. Post that the Naagin proceed to bite Raj, in the guise of kissing him. Raj dies a painful death.

Vijay and Sunita decide to marry. The Naagin attacks Sunita, at her house. But her friend manages to call Vijay. When the Naagin reaches Vijay, disguised as Sunita, Vijay knows she is the Naagin. Vijay takes her to a deserted mountain and throws her off the top. Unknown to Vijay, the Naagin changes shape and lands on a tree. Vijay goes back to the sage and returns the amulet. The Naagin attacks the sage, after Vijay is gone. She bites the sage after he tries to capture her. The sage release another Naag with a prayer to stop the Naagin from killing Vijay. The Naagin takes Sunita's form and tells Vijay that the Naagin is after her. Vijay looks at the Naag (sent by the sage) and shoots it thinking it is the Naagin. The Naagin, as Sunita, proceeds to seduce VIjay, but he sees her real form in the mirror. Anu is now living with Vijay, as he is her foster dad. He escapes with Anu onto the balcony and then to the roof of his house. From the roof he tries to rappel his way to the adjacent building, but the Naagin follows Vijay and Anu on the rappel ropes. The rope breaks and the Naagin falls to its death of a bed of nails on the ground, while Vijay and Anu land in a lower floor apartment breaking through the window.