Plot
On a dark night, Khanna (Hiralal), a wealthy man, hires an assassin to murder his rival, Seth Sohanlal. Khanna then makes a series of telephone calls to unknown people - to a doctor, whom he tells that a medical certificate needs to be made; to a mysterious young girl, whom he tells that the will needs to be sent to the "right place"; and to a lawyer, whom he tells that the will will reach him the next morning. Khanna later telephones Seth Sohanlal's niece, Asha (Nanda), and breaks the news of her uncle's death. The loud sobs and shrieks of a devastated Asha get amplified when she hears some gunshots at the other end of the line as another unseen man in a long coat and hat has entered Khanna's room and shot him point-blank. Khanna drops dead with his blood dripping strangely onto the receiver of the dangling telephone. A few days later, it is announced at a nightclub that the seven winners of a "lucky draw" have won a free fortnight-long trip to an unspecified destination abroad and will be going in a chartered airplane. These fortunate people are Barrister Rakesh (Pran), Dharamdas (Dhumal), Kishan (Manmohan), Kitty Kelly (Helen), Dr. Acharya (Madan Puri), Madhusudan Sharma (Tarun Bose), and finally, Asha, who now seems more composed.
Soon, these seven winners are in their chartered airplane, off of their vacation abroad, when the pilot announces to them and the only flight attendant who is on board, Anand (Manoj Kumar), that the airplane is forced to make an emergency landing at an anonymous remote island due to some technical problems. However, as soon as Anand and the seven passengers get off the airplane, the pilot shockingly dumps all their baggage out and the airplane takes off without them, leaving them all stranded on the island. At the same time, a mysterious, unseen woman begins singing an eerie song on the island without the woman ever being visible. The eight people follow the direction of the woman's voice, and finally arrive at a vast and spooky mansion, which seems to be unoccupied except for a comical lungi-clad butler (Mehmood), who is in charge of the mansion and has been weirdly expecting the arrival of the castaways. The butler also knows each of these people by name and has been provided with a letter listing all of these people except Anand. Further, everyone discovers that the butler has a diary which, besides containing an account of daily expense, also contains a message addressed to the entire group, accusing each of these people of having conspired to kill Seth Sohanlal and passing a death sentence on them.
That night, Anand, who himself has mysteriously brought with him a gun, discovers that Dr. Acharya has brought a bottle of poison and Dharamdas a fearsome-looking dagger. Rakesh and Kitty fall in love with each other, while the butler's suspicious actions indicate the presence of an unknown person in the mansion. The next day passes uneventfully, but at night, Anand and Asha are shocked to discover Kishan stabbed to death with a half-smoked cigar and a letter addressed to the group next to Kishan's dead body. The letter states that Kishan was the assassin hired by Khanna who killed Seth Sohanlal. The group deduces that Dharamdas murdered Kishan, but he pleads innocence and Anand and Asha also later discover him strangled to death. Rakesh accuses Dr. Acharya of having actually poisoned Dharamdas and it becomes clear that everyone was connected to Seth Sohanlal; Rakesh wrote Seth Sohanlal's will on Khanna's orders, while Kitty was Seth Sohanlal's private secretary who sent his will to Rakesh on Khanna's instructions, though neither knew about the other. The next day, Anand notices Rakesh hiding an axe before Dr. Acharya appears screaming that Sharma has been murdered with an axe. The murderer has left another letter next to Sharma's dead body stating that Sharma was Khanna's co-conspirator in Seth Sohanlal's murder. Now only three men - Anand, Rakesh and Dr. Acharya - and two women - Asha and Kitty - are left alive and terrified on the island along with the butler.
That night, Dr. Acharya catches the butler acting suspiciously and learns his secret before a scuffle ensues between them. In the presence of Asha and Kitty, a stabbed Dr. Acharya enters the dining room, utters Anand's name and breathes his last. Anand and Rakesh accuse each other of Dr. Acharya's murder while Asha begins questioning her faith in Anand. The next day, Kitty goes for a walk by herself and is strangled to death by a rope. Rakesh and Asha, searching for Kitty, are shocked to discover her dead body and Anand's hat next to it. Rakesh witnesses Anand running away from the crime scene and begins pursuing him but loses his trail. In a fit of rage, Rakesh tries to rape Asha in the mansion in the middle of the night. Asha escapes from Rakesh but runs into him again as Rakesh collapses dead with two daggers in his back. The lights in the mansion are switched off, which indicates that the killer has arrived and that Asha is next. The killer approaches Asha and she falls unconscious in fear, before the killer carries Asha to a secret room and brings her back to consciousness. At this point, Asha is shocked to discover that the killer is none other than Sharma, who reveals that he had only employed the butler to make the necessary arrangements on the island, and posing as one of the castaways, he killed Kishan and Dharamdas. He then convinced Dr. Acharya to declare him dead, on the pretext that it would help him find out the killer, and later killed Dr. Acharya as well with Kitty and Rakesh.
Just then, Anand appears at the scene and reveals that he is actually an undercover police inspector on the mission to capture Sharma, an escaped convict whose real name is Madanlal. Madanlal confesses to Anand and Asha that both Khanna and Seth Sohanlal were his partners in smuggling, but he was betrayed by them after being arrested by the police. Khanna and Seth Sohanlal raped Madanlal's sister too, which led her to commit suicide, and murdered Madanlal's brother after he informed Madanlal about their crime in prison. Khanna also had Seth Sohanlal killed to usurp the share of his money, but Madanlal escaped from prison and murdered Khanna. He then ensured that his targets "won" the lucky draw held at the nightclub and decided to take the trip to murder Khanna's remaining five assistants too. Madanlal then ties up both Anand and Asha and plays the game of Russian Roulette with them. However, the butler secretly arrives and unties Anand, who attacks Madanlal as he is about to shoot Asha with the only bullet. In the ensuing scuffle, Madanlal escapes from the mansion and runs towards the shore, but an airplane full of police officers is landed on the island and Madanlal is arrested for his crimes. The "ghost" woman who sings the ominous song turns out to be the butler's insane sister (Naina). The film ends with Anand, Asha, the butler and his sister leaving the ill-fated island on the airplane.
