Vaani awaits her marriage to her college boyfriend Mahesh at a court ceremony with her parents and younger brother. However, during the proceedings, she learns over a phone call that Mahesh has abandoned her for the daughter of a wealthy businessman, prioritizing his career over their relationship. Devastated, Vaani faints and subsequently withdraws into depression, isolating herself for months and abandoning her passion for writing.
Krish Kapoor, an aspiring musician struggling to establish himself, copes with childhood trauma and anger through music. Prone to emotional outbursts, he faces setbacks in his career, including clashes with journalists and disputes with his band members. His friend KV supports the band financially, despite the strain it places on his own education. Krish encounters Vaani when he returns her poetry notebook she accidentally left while applying for a job as a writer at a publishing house where he assaults a journalist, and is immediately drawn to the honesty and depth of her work.
Though initially hesitant about Krish’s erratic nature, Vaani agrees to collaborate with him on a song for hip-hop singer Prince. When she experiences creative difficulties, Krish discovers torn pages from her notebook, recognizing her inner struggles. To help her, he takes her to a cricket playground, a place of solace for him. Inspired by his focus, Vaani gradually resumes writing. Their collaboration grows into a friendship as they spend more time together, with Vaani regaining her confidence and Krish finding stability in her presence.
Their bond deepens after Krish confronts his alcoholic father, with whom he became estranged after his mother’s death. Vaani comforts him by opening up about her own heartache, and later encourages him to admit his father into rehabilitation. After completing their project, on which Krish is forced to cede all credit to pay for his father’s rehab, he distances himself, believing Vaani deserves better. However, they soon reunite at Prince’s concert, acknowledging their feelings for each other, and begin an intimate relationship. Krish reconciles with his band, and he and Vaani continue working together.
Vaani’s parents grow concerned upon witnessing Krish’s closeness to their daughter, fearing he may hurt her as Mahesh once did. The stress causes Vaani to collapse again, after which her mother questions Krish at the hospital about his intentions. When he promises commitment, her parents reluctantly approve of the relationship.
The couple’s lives change dramatically when Vaani is diagnosed with early-onset Alzheimer’s disease. Signs of memory loss become apparent, including a public breakdown during an encounter with Mahesh after he acquires Vaani’s workplace. Krish abandons his work commitments to support her, assuring her that he will remain by her side regardless of her condition. On medical advice, Vaani’s parents consider a change of environment for her new routine. Krish takes her to Alibaug, where they create new memories together.
At a later concert, Mahesh attempts to exploit Vaani’s vulnerability again during an episode of confusion. Krish intervenes, but Vaani, unable to recognize him, reacts fearfully and stabs him after he beats Mahesh, experiencing an even worse breakdown. Back at their guesthouse, Krish’s father reconciles with him, urging him not to repeat his mistakes. In a quiet moment, Krish plays the piano while Vaani composes the song “Saiyaara” as a farewell message, though she mistakenly calls him by Mahesh’s name. Soon after, she disappears.
Despite extensive searches, Vaani is not found. Krish releases “Saiyaara” in her memory, and the song becomes a global hit, propelling him to fame. He continues to carry Vaani’s writings with him while performing around India. Over a year later, KV discovers a viral video showing Vaani in Manali. Krish travels there and locates her at an ashram, where he receives a letter explaining she left to avoid hindering his career after remembering what happened at the concert, but admits she continued to follow his music from afar.
When Krish reunites with her, Vaani no longer recognizes him and is beginning to shut herself off from the world. He reminds her of their shared memories, including their first moments at the cricket playground. Slowly, fragments of her memory return, and she ultimately recalls their love. The film concludes with Krish performing at Wembley Stadium, with Vaani by his side as they marry, signifying their reunion through love, music, and memory. Vaani resumes writing as she reflects on their wedding.