Dr. Sethuraman is a brilliant scientist and renowned watchmaker who lives with his wife Priya and newborn son Manikandan. He has devoted himself to inventing a time machine using a watch. In January 1990, Sethuraman manages to successfully complete his invention, although it was only capable of moving back and forth in time for 24 hours. His happiness is short-lived, however, as his evil twin brother Athreya attacks the family and kills Priya to get the watch. He manages to find the key to the box that the watch was hidden in, but not the box. Unable to use the watch and fearful for his son’s life, an injured Sethuraman manages to escape with his son and gets on a train, with Athreya in close pursuit. Sethuraman pleads with a woman he met on the train named Sathyabhama to take care of his son and goes to face Athreya. He manages to trick Athreya into thinking he’s carrying a bomb, prompting Athreya to quickly kill Sethuraman before jumping off the train to his apparent death.

26 years later, Manikandan (Mani) is now a talented watch mechanic who believes Sathyabhama to be his mother. It is revealed that Sethuraman placed the locked box containing his watch along with Mani, who grew up unaware of the contents of the box, as well as his true parents. Mani meets a girl Sathya and falls in love with her. Somewhere else, Athreya, who survived his fall and was in a coma, wakes up after 26 years and is shocked to find out that he is now paralysed from the waist down and significantly older. He is cared for by his trusted confidante, Mithran.

Through an incredible set of coincidences, the key to the box ends up in the hands of Mani, who unlocks the box and discovers the watch inside. He figures out its incredible capabilities including its ability to freeze time for 30 seconds, but questions the origin of the watch, and how it ended up in his possession.

Athreya, upset with the fact that he lost 26 years of his life and has become a paraplegic, obsesses over the watch and wishes to go back in time to relive his lost youth. Mithran issues an advertisement offering INR 5 crores (50 million) as a reward for the lost watch. Mani deduces that the creator of the advertisement is aware of the powers of the watch. In order to figure out the truth, Mani uses the original to make an identical copy and along with his friend, goes to the provided address.

At the office, Athreya spots Mani’s copy among countless others and realises that Mani has the original watch. He summons both of them to the office and viciously attacks them, kills Mani, and gets hold of the watch. An ecstatic Athreya reverses time only to find out that the watch cannot transport its wearer beyond 24 hours, waking up at 12 am the night before. He now realises that Mani is the only one who can upgrade the watch. Since the day’s events have reversed, Mani is still alive and their confrontation at the office is yet to occur. Athreya then decides to convince Mani that he is Sethuraman, and lie that he is dying from an incurable disease.

Now disguised as Sethuraman, Athreya finds Mani and tricks him to upgrade the watch to enable larger time jumps. Mani manages to successfully upgrade the watch but learns Athreya’s true identity and the reason for his parent’s death. Mani tricks Athreya into revealing the date of his parent’s death and returns to 1990 to warn them. Sethuraman discovers the upgraded watch and realises that Mani has travelled back in time to warn them. Now prepared, Sethuraman manages to successfully use his watch to freeze time, kill Athreya and escape his henchmen. Priya asks Sethu to throw the watch away as she has had enough of the past to which he complies.

Sethu and Priya board the same train as Sathyabhama, and they start a conversation in which Sethu tells Sathyabama that he is a physics teacher to which she asked them to come and join her family's school as they want to hire a physics teacher. Sethu and Priya, for a fresh and happy start, agree to it. The film ends with a young Mani talking to a young Sathya.