Plot
In September 2022, newlyweds Karthik and Anu move into their own second-hand flat after Karthik strives hard to buy it. Anu starts noticing eerie happenings, such as taps turning on and off and switches operating involuntarily. She enquires with the neighbours about any unnatural deaths in the flats. A vegetable vendor mentions one such incident in the same block, when a family went missing without a trace. Anu discovers a child-like drawing on their bedroom wall, hidden behind the bureau. The drawings keep changing and increasing every day. Karthik dismisses her concerns and berates her when she suggests moving out. Around the same time, Karthik also begins noticing the strange occurrences.
Meanwhile, Mahi, a young boy, is playing alone in his flat. He notices movement inside their bureau, and when he tries to investigate, an invisible force pushes him inside. Terrified, he develops a psychogenic fever. The doctor listens to his story. While his parents do not believe him, the doctor suggests he send a message to the "ghost," and if he gets a response, everyone will believe him. Mahi follows the advice and writes a message on his bedroom wall.
This message appears on Anu and Karthik's bedroom wall, terrifying them. They respond, and their reply appears on the wall in Mahi’s flat. Though initially frightened, both families eventually realize they are not communicating with ghosts but with another family living elsewhere. It is revealed that Mahi and his family are living in the same flat "F1" in the same building, but in the year September 2012. Sometime between September 2012 and September 2022, they had sold the flat, which Karthik later bought. The families consult physicists in their respective timelines, who explain that this may have occurred due to a "tesseract," creating a bridge between the two years, possibly triggered by a strong negative charged force such as lightning.
The families gradually adapt to the unintentional interference from one another. However, problems arise when Ramesh (Mahi's father), an expert electrician, attempts to retrofit the wiring to separate the electrical connections of the two timelines. Karthik unknowingly switches the power back on in 2022, injuring Ramesh. The constant disturbances leave Karthik sleepless, and he loses his job after dozing off at work and causing a fire accident. These incidents strain the relationship between the two families.
Both families contemplate selling the flat to avoid further hardship. Every attempt by Karthik to sell is thwarted by the unintended interference of Ramesh’s family. Eventually, both Ramesh and Karthik independently begin searching for each other in their respective timelines.
Karthik learns that Ramesh sold the flat in 2013, closed his shop, and began working in a factory in Ambattur. He locates Ramesh and tries to explain, but Ramesh does not recognize him. Karthik’s friend informs him that the tesseract has created a new timeline for Ramesh and his family, and the Ramesh he found in 2022 is not the same one he has been communicating with in 2012. Still, Karthik hopes the 2022 Ramesh can help and invites him to visit, mentioning that it is the same house Ramesh lived in during 2012. Ramesh agrees.
In 2012, Ramesh finds Karthik working as a pizza delivery driver and asks him to visit his home around 9 PM. Karthik reluctantly agrees.
In 2022, Ramesh and his wife visit Karthik's flat and communicate with their past selves through the wall. It is then revealed that Mahi had died in a freak accident in 2012, and the accident occurred on that very date. 2022 Ramesh begs his 2012 self to immediately find Mahi. The 2012 Ramesh and his wife rush out without reading the final message from 2022, which mentioned the exact location where Mahi was playing.
In 2012, Ramesh and his wife frantically search for Mahi, losing precious time. Meanwhile, Mahi climbs a tree in the apartment park to retrieve a toy helicopter and ends up dangling precariously from a branch. Ramesh hears Mahi’s cries and runs toward him. At the same time, a nearby biker notices the boy’s danger and springs into action, breaking his fall and saving him from injury.
2022 Ramesh receives a message from the past that Mahi has been saved—by none other than 2012 Karthik, who had come to see Ramesh earlier that day. Though Ramesh and his wife of 2022 no longer have their son, they find solace in knowing that an alternate version of themselves still does.
Karthik and Anu decide to vacate the flat and hand it over to Ramesh and his wife, so that they can remain in touch with their son from the other timeline through the wall.
