The film's plot is inspired by the 2007 Thai movie Alone which itself is loosely based on Agatha Christie's novel Elephants Can Remember.

[1][2][3][4] Internationally famous Indian sharp shooter Nadiya Mether catches Sauparnika Express, a train on its inaugural run between Chennai and Mangalore.

The passengers in the compartment during the inaugural journey apart from the three victims were an actress Priya Rose, her mother Rajamma and father, four doctors returning from a medical conference, a Tamil Novelist Seetharaman, Palakkad Railway SP Alexander, Madhavan Master, his wife and their mentally unstable son Balachandran "Balu".

As the train reaches Madukarai station, Balu is spotted with a blade in hand apparently after stabbing Nadiya who goes unconscious.

Upon questioning Muthuraj, he reveals to Sharafuddeen about meeting an additional passenger that night, who is identified as Lakkidi Manikandan, a killer in disguise of a police constable.

She also tells that during the journey, Priya inadvertently ran into Madhavan who is angry at her as well as her mother who are responsible for Balu's mental problems.

Since the reasons given by him are unconvincing, Sharafuddeen attempts to torture him that forces Sundaran to reveal the truth - he committed the murder of Thulasimani on the orders of his boss, the division manager Vijayabhanu.

Nadira grew up to be a professional dancer, while Nadiya became an acclaimed shooter, holding a grudge against Sharaufuddeen for killing her father before her eyes.

While doctors confirmed that chances of Nadiya recovering from her coma are very less, Ustad even asks Nadira to sign consent paper for mercy killing of her sister, which she refuses.

When Nadira arrives, Sharafuddeen reveals in front of her that Aadilakshmi was always after Janaki Iyer's family wealth which is now entitled primarily to Nadiya, as Janaki Iyer had made Nadiya the heir to the majority her property, including her art academy and Nadira the heir to her art and dance legacy.

Sharafudeen says that, if not Aadi Lakshmi's brother it has to be Zia Musafir who might have done this, by taking a break from his world tour, as he was not reportedly in Bahamas on the day Nadiya was stabbed and was in India as per Emigration records.

Despite initially objecting to Sharafuddeen's claim, Nadiya's identity is revealed due to her characteristic trait of getting a nosebleed whenever she is angry or upset.

The truth was that Nadiya - the shooter was deep in love with Zia, though he had affection only towards her identical twin sister Nadira - the dancer.

Ustad and Janaki Iyer fixed the marriage without the consent of Nadiya and she was provoked to mad anger when Nadira boasted about Zia's love to her.

Soon after her confession to Sharafuddeen, she jumps out of the moving train and hits hard on to a railway signal thereby killing herself, which makes it the real night of Nadiya's death.

Months later, Zia returns and takes Nadira, who is in a vegetative state, to the US for advanced treatment hoping that she will recover.