In 1990, Sethuraman, a brilliant scientist and skilled watchmaker, shared a life with his wife Priya and their newborn son, Manikandan. On January 13, he achieved a significant milestone by completing his invention, a time-traveling watch known as Project 24. Sadly, his moment of joy was abruptly cut short when his criminal twin brother, Athreya, violently intruded upon their lives, killing Priya in a desperate attempt to seize the watch. In the chaos, Sethuraman manages to escape with his son, but not before Athreya discovers only the key to where the watch was hidden. Fearful for Manikandan's safety and wounded from the ordeal, Sethuraman boards a train and implores Sathyabama, a woman he meets during the journey, to protect his son. In a moment of brave deception, he tricks Athreya into believing he is holding a bomb, which leads to his own death while allowing Manikandan to escape. Unbeknownst to him, Sethuraman secures the locked box that contains the watch, while his son grows up ignorant of his true heritage.
Fast forward to 2016, Manikandan has evolved into a skilled watch mechanic, believing Sathyabama to be his mother. His life takes a romantic turn when he encounters Sathya, a young woman who visits him for a watch repair, and quickly falls for her. Meanwhile, Athreya unexpectedly awakens from a 26-year coma, triggered by a fire at the hospital where he was recuperating, only to discover he is now paralyzed from the waist down. His days are spent under the watchful care of his loyal associate, Mithran.
A twist of fate brings the key to the box into Mani's possession. Upon opening it, he is astounded to uncover the watch inside, which has the power to freeze time for brief periods, though he remains puzzled about its origins and how it came to him. Athreya, plagued by his newfound limitations and lost years, becomes fixated on the watch, eager to turn back the clock and reclaim his youth. In a desperate bid, Mithran places an advertisement promising a bounty of INR 5 crores for the lost piece. This ad captures the attention of Saravanan, a friend of Mani's, leading to suspicions about whether the creator knows the watch’s true capabilities. To get to the bottom of it, Mani crafts a replica of the original watch and, accompanied by Saravanan, seeks out the provided address.
Upon arrival at the office, Athreya spots the imitation and realizes that Mani possesses the original watch. A violent confrontation ensues, culminating in Athreya brutally murdering Mani before seizing the watch. In a moment of triumph, Athreya attempts to reverse time, only to discover that the watch is limited to 24-hour jumps, forcing him to reawaken the night before. In this twisted turn of events, it becomes clear that only Mani can enhance the watch’s potential.
Athreya, now impersonating Sethuraman, sets out to manipulate Mani into upgrading the device under the pretense of being his father who is terminally ill. As Mani carries out the upgrade, he uncovers the truth about Athreya's identity and his family's demise. Crafty and determined, he tricks Athreya into revealing the date of his parents’ deaths and embarks on a journey back to 1990 to alert them. However, moments before his time travel, Athreya clings to the watch, resulting in both being transported back to the past: Athreya manifesting as a robust adult ready to confront Sethuraman, and Mani as an infant, incapable of speech.
Sethuraman comes across the upgraded watch in his child's crib. Initially thrilled that Manikandan has time-traveled, Priya questions why he would return to a time when he could not communicate. It dawns on them both that the return stems from a desire to warn them. Acting swiftly, Sethuraman uses the watch to freeze time, confronts and eliminates Athreya, and manages to escape his henchmen. Priya, weary of the past, implores Sethu to discard the watch, which he reluctantly agrees to do.
They take a new train, alongside Sathyabama, embarking on fresh beginnings as they converse. Sethuraman shares that he now identifies as a science teacher, leading Sathyabama to extend a job offer at her family's school, which they happily accept.
As the credits roll, a nostalgic scene unfolds featuring a young Mani engaging with a young Sathya, hinting at their intertwined fates.
