Kabir Malhotra (Anupam Kher) is a billionaire tycoon who invites four people to his island home in Greece. None of these people have ever met each other before, and Kabir sends a different letter to each, luring them with different promises. These four people are:
Neil Menon (Abhishek Bachchan), a casino owner in Turkey. He has financial problems with mob bosses that Kabir offers to help with.
Vikram Kapoor (Jimmy Shergill), an actor with drug and career problems. Kabir writes to him that he wants to finance the biggest film ever made, and offers Vikram a role in it.
OP Ramsay (Boman Irani), a political leader in Thailand. His campaign is under threat of scandal, and Kabir offers to provide new funding to him.
Tisha Khanna (Shahana Goswami), a crime journalist in the United Kingdom who is looking for her big break. Kabir writes to her saying that he has a huge story on his hands and invites her to cover it.
The four individuals arrive at the island, where they are greeted by Kabir's personal assistant Samara Shroff (Gauhar Khan) who takes them into a dining room that is being secretly filmed. There, Kabir reveals that he has invited all of them because of their link to his daughter, Maya (Sarah-Jane Dias), whom Kabir has spent years trying to find. Maya was trafficked as a child by OP Ramsay, as an adult brought into the crime world by Neil Menon, and in the end killed in a car accident by Vikram Kapoor. Kabir has gathered evidence against all three of them and has invited the International Vigilance Squad (IVS) to the island to arrest them. Tisha Khanna, the only innocent one of the group, was invited because, previously unknown to her, she is Maya's fraternal twin sister and Kabir's only remaining biological child. Tisha rejects Kabir's attempts to forge a relationship with her, claiming that she doesn't want his fortune.
Unable to escape the island, the group await the arrival of the IVS. In the morning, they hear what sounds like a gunshot from Kabir's room. They find Kabir Malhotra dead in his study, seemingly having committed suicide with a gun.
The IVS, led by Sia Agnihotri (Kangna Ranaut), arrive at the island. She watches the video of the previous night's reveal by Kabir Malhotra to the guests, but as they are unable to find the evidence that Kabir claimed to have, they let the guests go. The case is declared a suicide, but Sia puts all four guests under surveillance.
Through flashback, it is revealed that Neil was in love with Maya, who saved his life during a shootout at his casino. In the present day, Neil decides to take revenge on OP Ramsay and Vikram for what they did to her. Neil tricks both of them into giving public confessions about their crimes. Vikram commits suicide and OP Ramsay dies of a heart attack (his medication having been stolen by Neil). Sia, who has been monitoring Vikram and OP Ramsay, knows that Neil is responsible.
It is then revealed that Neil is also on the IVS, real name is Arjun Singhania, but has been under deep cover for many years. He, too, doesn't believe that Kabir committed suicide, and decides to work together with Sia to find the true culprit. Neil noticed that Kabir was left-handed, yet the gun that killed him was in his right hand.
Tisha, as Kabir Malhotra's only child, is to inherit everything of Kabir's fortune. However, Neil and Sia receive news that Tisha attempted suicide. When she wakes up, she tells them that it wasn't suicide, but someone attacked her in her house. Meanwhile, Neil has found that Kabir has a brother, Iqbal, who is next in line to inherit his fortune. Sia and Neil travel to the missionary where Iqbal is currently living, but they find him too ill to speak to them. A nurse tells them that Iqbal had a daughter who died, but Neil notices that there are letters sent to him dated after her supposed to death, so she must still be alive.
Neil and Sia travel back to the island, where they confront the late Kabir's personal assistant, Samara. It is revealed that Samara is Kabir's biological niece, though Kabir never knew. Neil realized that there was foul play when, at the missionary, he saw a picture of Kabir and Iqbal when they were children, and they were identical twins. The man in the missionary could not have been Kabir's brother. After shooting Sia on shoulder but not killed, Iqbal reveals himself pointing the gun at Neil. Samara grabs Sia's gun, lying on the ground and points at Neil. Iqbal explains that he has been working with his daughter to get Kabir's fortune. Tisha was a surprise they hadn't anticipated, so they had to take her out of the picture. They used Kabir's three guilty guests in order to deflect suspicion from Samara, predicting correctly that the police would suspect one of the guests as responsible for Kabir's murder. Iqbal orders Samara to get out and wait for him at the boat. When she tries to leave Neil hit her hands making her turn around and pointing gun at Iqbal. As Samara covers Neil, Iqbal cannot aim him. Behind Samara, Neil pulls triggers of Samara's gun, shooting Iqbal and killing him. Samara get arrested for the murder and other criminal charges.
In the end, Sia and Neil joking around, she ask him does he ever been serious in life. He replies ek baar (once) remembering Maya.