Gumnaam (1965)

After murdering a rich man named Sohanlal and covering it up as a car accident, a man named Khanna, who ordered the hit, is murdered as well, by someone he is shocked to see. It is revealed that Sohanlal's murder was actually a conspiracy of many people, also unknown. Before dying, Khanna has told the news of Sohanlal's death to his niece Asha. Some days later, seven people, including Asha, win a trip to an island in a chartered plane, courtesy a lucky draw in a gala. The others winners are one Barrister Rakesh, one Dharamdas, one Kishan, one Dr. Acharya, one Madhusudan Sharma and one Kitty Kelly. The seven people go to the island, with one Anand, who happens to be a crew member in the chartered plane.

Suddenly, the plane develops a snag, causing it to cause an emergency landing. Along with Anand, all the winners leave the plane, along with their personal belongings. However, everyone is amazed when the plane suddenly starts and the pilot flies away, stranding them on the island. Unable to understand what is happening, everybody tries to scout the place unsuccessfully. Suddenly, a woman starts singing an ominous song. Partly trying to find the woman and partly trying to find the place where they were supposed to stay, they finally reach their destination, where they meet the butler. Later on the dinner table, Dharamdas spots a diary, which seems innocuous to him, but Anand's facial expressions grow serious on reading the diary's contents.

Anand reads the diaries contents to all of them, which reveals that they are all connected to a crime and responsible for it. The writer of the diary says that he is going to kill all of them, one per day. The butler claims that he knows nothing about the singing lady. As everybody retires to their rooms, Anand spies on them, finding out that the doctor has brought a bottle of poison with him and that Dharamdas has a revolver. Kishan catches him in the act, but does nothing. Meanwhile, the butler too is acting suspicious, and his actions prove that there is at least one more person in the house. The very next day, Kishan spots a ship. He, Kitty and Dr Acharya try to signal the ship, but in vain.

Meanwhile, Anand starts flirting with Asha. Rakesh and Kitty too take a shine for each other. Although everyone is suspicious of each other, Rakesh has Anand at number one on his list. That night, Kishan is murdered and his body is found by Anand and Asha. The killer has planted a note saying that Kishan was a killer who killed Sohanlal. It quickly becomes clear that the people know something about Sohanlal. Dharamdas seems to be the guilty party based on the deductions. He pleads innocence, upon which Mr. Sharma asks everybody to give him one day to prove his innocence. The very next night, Dharamdas is found dead by Anand and Asha. Anand believes that the villain is amongst them, while Rakesh believes that Dharamdas was poisoned and the doctor is the culprit, based on what he saw.

It is clear that any one of the four remaining men could be the killer. Kitty is revealed to be Sohanlal's personal secretary while Rakesh is the lawyer who had created the will on Khanna's orders. It is also revealed that Kitty was the one who sent the papers to Rakesh as instructed by Khanna, although neither knew about each other. Asha has her own suspicions on Anand, who clams up when she asks information about him. While talking to her, Anand spots Rakesh hiding an axe. Soon, the doctor arrives screaming that Sharma has been killed. It is clear that Sharma has been axed to death. The killer has sent another letter, accusing Sharma to be the co-conspirator of Khanna in the murder.

Anand accuses Rakesh of the murder, while Rakesh is now unsure about Anand's guilt. The doctor later catches butler engaging in a suspicious activity, indicating that he knows the butler's secret now. A scuffle between the duo follows. While Asha and Kitty are in the dining room, the doctor enters and falls down, indicating that he has been stabbed. Before dying, he manages to take Anand's name. Rakesh The now believes that Anand is the killer, which Anand denies. Asha, who begins to question her faith in Anand, ends up drinking with Kitty. Anand and Asha have a fight over this. The next day, Rakesh advises Asha to not to go alone anywhere. Asha reveals to him that she is searching for Kitty. Sensing something amiss, the duo go to find her.

Kitty has gone to swim, but senses that she is not alone. She starts running, but the unseen killer corners her and hangs her by a tree. Rakesh and Asha arrive at the scene too late, but his suspicion is confirmed on seeing Anand's hat next to Kitty's hanged body. Rakesh starts chasing Anand, but loses the trail. In rage, he trturns back to the mansion, where he tries to rape Asha as a revenge. Asha somehow escapes his clutches and runs in the building, but runs into Rakesh again, just as he falls down, revealing two daggers in his chest. With this horrifying development, she loses her calm. At the very same moment, the lights in the mansion go out, indicating that the killer is here and she is the next target.

As the killer, who can not be seen now due to darkness, approaches Asha, she faints. He lifts her and enters a secret room in the building, which leads downstairs. He brings her back to consciousness, upon which she starts screaming for Anand. Now, the criminal turns to her and is revealed to be Madhusudan Sharma. He reveals that Anand was growing suspicious of him, following which he had to take the doctor in his confidence. The doctor lied that he was dead and to tie the loose end, he killed the doctor before resuming his spree. Sharma also gets a shock of his life himself on seeing Anand in the secret room. Now, it is revealed that Anand is Inspector Anand, while Sharma is actually an escaped convict named Madanlal.

Madanlal succeeds in overpowering both Anand and Asha, and ties them. He explains them the whole story: he, Khanna and Sohanlal were smugglers. Once, Madanlal got caught, while his partners convinced him to take all the blame on himself. However, after he went to jail, Sohanlal raped Madanlal's sister, who committed suicide. Madanlal's brother, who informed him about the treachery, was also killed by the duo. Khanna, who later grew greedy, had Sohanlal killed to usurp his money. Every person he killed till now was a party in the plan to murder Sohanlal. Anand knows more than Madanlal thinks: the "ghost" singing the song is actually the butler's mentally unstable sister, whom the butler had secretly brought here, Madanlal killed Khanna and then saw to it that everybody including Asha got the lucky tickets.

Meanwhile, Madanlal plays a game of Russian Roulette with Anand and Asha, while the butler sneaks in and stealthily frees Anand. When it is clear that Asha will get the bullet, Anand suddenly attacks Madanlal. In a melee that occurs, Madanlal escapes from the mansion and runs towards the shore, with other on his pursuit. A plane comes, which he tries to stop. As he runs towards the plane, it is revealed that there were police in it, who promptly arrest him. Anand and Asha board the plane along with the now free butler and his sister.