In the middle of the night, Indhiran, accompanied by his friends Sathish and Karuna, buys a gun illegally from a local gangster. Back home, Indhiran stares at his wish list and recalls his past.
Past: Since childhood, Indhiran has narcolepsy, a rare disorder that makes him fall asleep whenever his emotions reach an extreme level, preventing him from living a normal life. He needs to be escorted at all times, despite excelling in academics, and he cannot impregnate women because he falls asleep during sex, though he can still hear everything said while he sleeps. To cope, he builds a bucket list of goals he wants to achieve on his own. One day, he ventures out alone, ticking off a goal, but when a vehicle nearly hits him while crossing the road, fear triggers a sudden sleep.
A passerby makes him pose as an orphaned corpse and gathers money from onlookers for his burial. Meera, who passes by, takes pity and shells out almost five thousand rupees. Later, Meera meets Indhiran in a shopping mall and faints from shock upon seeing him alive. After clearing the misunderstanding, they start dating and fall for each other. Meera makes one of Indhiran's dreams come true by kissing him, but her father Jayaprakash opposes their marriage as Indhiran cannot stay awake during sex. Meera urges Indhiran to find a way to stay awake. It dawns on Indhiran that he had never fallen asleep while taking a shower. Believing that her father will accept Indhiran only when his sexual potency is proved, Meera and Indhiran have sex in his swimming pool, resulting in Meera becoming pregnant.
On a late-night drive, Meera drives her car on an under-construction bridge. Meera's car is hit by another, and the shock makes Indhiran doze off while Meera is attacked and raped by unknown thugs. Indhiran can hear the entire ordeal but remains asleep, and he sheds a tear for being helpless. Meera falls into a coma, and her child is aborted. A heartbroken Indhiran vows to exact revenge on the perpetrators.
Present: Deciding to exact vengeance all by himself, Indhiran fails to testify to the police. He begins to question people who knew Meera. Inquiring Meera's friends, Indhiran first suspects Karthik, a rich but ill-mannered guy whose marriage proposal was rejected by Meera. Indhiran confronts him, but he denies any knowledge about the incident, even offering to help Indhiran if required. Indhiran realises that the sound of sudden obstacles makes him sleep. To prevent this, he buys a portable audio player and uses it with full volume. A transformer explosion right next to him has no effect on him because of the music, and thus he realises his newfound advantage.
Indhiran also reaches out to a meditation teacher who teaches him about staying calm and being immune to shock by anticipating the event in advance. He stays awake a full night and tries to control his sleep by standing between two loud trains with the audio player playing at full volume. After obtaining control, Indhiran gets information from a sympathetic police officer regarding attack cases to find a lead. He remembers one of the thugs' name Sekhar and his ringtone, while the police find out that the criminals drove a red car. Indhiran stumbles upon a red car at a petrol bunk and inquires the driver, who claims that the car was with a mechanic named Sekhar on the day the crime took place.
At the workshop, Indhiran spots the mechanic who tries to run upon recognizing Indhiran, and a chase ensues, leading them to a building under construction. Informed by [Sathish], Karuna arrives there and kills Sekhar. He then injures himself to convince Indhiran that he was assaulted by Sekhar who escaped the scene. He is then admitted for treatment.
Past: Married to Karuna for two years, Kavitha was dissatisfied with her drunkard husband; she begins an affair with Aravind, a wealthy friend of Karuna. He spends a lot of money buying her expensive gifts. Indhiran gains knowledge of this and advises Kavitha against it. It turns out that Karuna, to realise his ambitions of running a business in the US, had been using his wife to manipulate Aravind. Citing Indhiran's confrontation, Kavitha lied to Aravind that if Karuna learns of their affair, he would kill them both. She suggested that the only way to solve it once and for all is to arrange ₹ 20 million that Karuna needs to settle in the US. With him gone, they could enjoy being together. Aravind agreed to finance Karuna out of his lust for her.
Later, when Karuna and Kavitha are celebrating their success, Indhiran drops by unexpectedly. Indhiran suspects them and informs Aravind, who confronts the couple. When Aravind realises that he had been cheated, he hits Kavitha in a fit of rage, and she dies after the hit lands her head on the corner of a cupboard. Infuriated, Karuna retaliates and kills Aravind. Karuna arranges for disposing of the two bodies with the help of the thugs and lies to Indhiran that Kavitha has eloped with Aravind. Since he assumed that Indhiran was responsible for Kavitha's death, Karuna had planned to take vengeance by making him suffer the same way and requested the thugs to attack Meera.
Present: The remaining thugs insist Karuna to bring Indhiran to the same place where Sekhar was killed. Finding out that it was Karuna who had killed Sekhar, they beat him up. When Indhiran arrives, the thugs remove the audio player from Indhiran, who gets an adrenaline rush and dozes off. While the thugs are thrashing him, one of them breaks a water pump, which splashes water all over and awakens Indhiran, who kills them all, except Karuna. Indhiran says that he had seen Karuna killing Sekhar. When Indhiran questions Karuna as to why he sent thugs to attack Meera, Karuna angrily tells him that it was revenge for Kavitha's death, which was caused by Indhiran telling Aravind the truth.
Karuna angrily attacks Indhiran and Indhiran retaliates by hitting Karuna violently. Despite feeling bad for his friend and hesitant to kill him due to their close friendship, he remembers Meera and kills Karuna by kicking him into a steel bar. With all his wishes fulfilled, Indhiran has a new wish that he would help Meera recover soon. The final scene shows Indhiran hugging Meera, who is tearful hearing him, which shows that she is definitely recovering.
