Pradeep, a support engineer at Cognizant in Chennai, lives with his widowed mother Saraswathi and elder sister Divya. He is in a romantic relationship with Nikitha, a software engineer at Infosys and the daughter of Venu Shastri, a strict and eccentric lawyer. Though they wish to marry, Pradeep hesitates because of Venu's rigid nature. When Venu discovers their relationship, he invites Pradeep home, pretending to discuss marriage but instead proposes a challenge: Pradeep and Nikitha must swap phones for 24 hours with full access. If they remain in love afterward, he will approve their marriage. They reluctantly agree, and Pradeep, having sanitised his WhatsApp messages, feels relieved.
Pradeep returns home to manage Divya's upcoming wedding to Yogi, a mild-mannered dentist. Encouraged by friends, Pradeep checks Nikitha's phone and finds chats with Revi, her male best friend who has a one-sided love for her, and messages from her ex-boyfriend Mamakutty. He is further upset to learn that Nikitha had recently gone on a night drive to Puducherry with Mamakutty, lying to Pradeep. A confrontation follows, straining their relationship. Pradeep then proposes extending the phone swap until Divya's wedding, which Venu readily agrees to, secretly asking Nikitha to restore Pradeep's deleted WhatsApp messages.
Meanwhile, Divya becomes suspicious of Yogi's secretive behaviour with his phone. Learning about Pradeep's phone swap, she proposes the same with Yogi, who refuses. Multiple failed attempts to access Yogi's phone further strain their relationship.
Nikitha soon discovers Pradeep's porn addiction and flirtatious chats with multiple girls, including efforts to solicit photos under the pretext of offering acting opportunities. Unknown to her, Pradeep has a secret Instagram account, created by himself and friends during college for explicit messaging using a fake female identity. This account had even messaged Nikitha and her younger sister Shwetha, though Pradeep himself was not the sender. Fearing exposure and legal trouble, Pradeep meets Nikitha at a restaurant to retrieve his phone and log out of the account. Yogi overhears Pradeep's friends discussing the issue and advises them to log out from another device using an OTP.
Revi intercepts the OTP and exposes Pradeep, leading to a heated argument and their break-up. Pradeep, furious at Revi's interference, assaults him but is stopped by restaurant staff. Later, during Divya's wedding reception, Pradeep suspects his friend Mani of operating the account and blames him, despite Mani's denials.
Amidst this turmoil, Divya and Yogi argue over the latter's phone secrecy. In frustration, Pradeep attempts to snatch Yogi's phone but is stopped by Saraswathi. Breaking down, he confides in his mother about his break-up. Saraswathi consoles him, emphasising the importance of trust in relationships. Yogi later reveals to Pradeep that he hid his phone due to embarrassment over being mocked for his overweight appearance. He feared Divya would reject him if she saw the ridicule he faced. Overhearing this, Divya appreciates Yogi's vulnerability and reconciles with him, deciding not to look at his phone. Pradeep also patches up with Mani and his friends.
Meanwhile, a pornographic video, seemingly involving Nikitha, goes viral. Venu, believing the video, assaults and disowns her, despite her pleas that it is fake. Heartbroken, Nikitha leaves home. Pradeep, with the help of his friends, try to locate Nikitha but to no avail. He then stumbles upon a mango tree whose seed he had planted in his childhood — a young Pradeep used to cry as his mango tree failed to germinate as he used to take out the seed everyday. His mother tells him not to take the seed out everyday and have some faith. He realizes this and then deduces Nikitha's whereabouts and finds her sitting alone at a beach. Pradeep consoles her and reveals that he and his friends tracked down the perpetrator: Nikitha's publicity-loving colleague Kaushik, who had created a deepfake video for online attention. Kaushik is arrested, and Pradeep and Nikitha reconcile. Venu apologises for his mistrust and reveals the true purpose of the phone swap—to test the strength of their relationship. Seeing they have overcome all hurdles, he blesses their marriage. However, who sent the obscene messages to Nikitha and Shwetha from the fake account, remains unknown.
The film ends with the message that trust is the foundation of peace in relationship.
