A fateful encounter between Ayan Sanger (Ranbir Kapoor) and Alizeh Khan (Anushka Sharma) leads to a spontaneous kiss, albeit one that Alizeh later critiques, stating that their chemistry feels off. Both are navigating rocky waters in their relationships; Ayan, who disapproves of his girlfriend Lisa's attire at a party, and Alizeh, who is juggling life as the youngest daughter in a wealthy family of four. While Ayan is pursuing an MBA, he secretly dreams of becoming a singer, a passion that doesn’t sit well with his father. In contrast, Alizeh is embracing a life of freedom, shying away from commitment.
Alizeh reminisces about her past crush, Ali, whom she adored during her college days in Lucknow. However, her infatuation crumbled when he chose to date an air hostess, leaving her heartbroken and leading her to London. During a dare-driven double date, Alizeh confronts Lisa, whom she views as a gold-digger, resulting in a dramatic outburst involving spilled wine. Despite these turbulent interactions, Ayan and Alizeh bond over their shared affection for classic 80s Bollywood songs, sparking an unexpected connection.
With Alizeh engaging Ayan's wilder side, they frequently find themselves at discos, restaurants, and exploring the streets of Paris on a trip together. Even as Ayan develops deeper feelings for Alizeh, she sees him merely as a friend. This dynamic shifts when Alizeh unexpectedly encounters her ex, Ali (Fawad Khan), who wishes to revive their relationship. Torn, Alizeh makes the difficult decision to send Ayan back to London, leading to a cessation of their communication.
Days later, Alizeh contacts Ayan to invite him to her wedding with Ali in Lucknow. Upon hearing the news, Ayan is devastated, yet he attends the ceremony where he professes his love to Alizeh—only to be rejected, leaving him heartbroken.
While at the airport, Ayan meets Saba (Aishwarya Rai), a poetess bound for Vienna. Confiding in her about his pain, Saba offers solace, handing him a note with her poetry and contact information. Three months later, Ayan reaches out, and they reconnect at a disco, eventually sharing a night of intimacy. However, Ayan discovers that Saba, having gone through a divorce, is solely interested in a physical relationship.
Ayan also encounters Saba's ex-husband Tahir Taliyar Khan (Shah Rukh Khan), who shares profound insights about love, stressing that it can be empowering rather than a weakness. Determined to forget Alizeh, Ayan blocks her on all platforms but later finds himself reaching out again, to stir feelings of jealousy by sending Saba’s pictures.
When Alizeh reveals she is coming to Vienna, Ayan invites her for dinner, blissfully unaware of Alizeh's mixed feelings. Saba, meanwhile, begins to have feelings for Ayan, yet his heart still belongs to Alizeh. Becoming a successful singer, Ayan has a chance encounter with Ali, realizing that his relationship with Alizeh has ended.
In a poignant moment, Ayan waits at Alizeh's favorite spot, only to receive devastating news: she has been diagnosed with Stage 4 cancer and has limited time left. The two attempt to cherish their final moments together, with Ayan desperately trying to win her heart. However, Alizeh is resolute in her decision, leading to a painful argument that causes her to distance herself.
Eventually, Ayan comes to terms with the reality that they can only remain friends. The narrative loops back to Ayan, now an acclaimed singer, reflecting on the love of his life. He gives an interview dedicated to Alizeh, who has passed away, performing the touching song "Channa Mereya," which draws inspiration from their shared story.
