Hum Tum is a romantic comedy-drama. The movie revolves around Karan Kapoor (Saif Ali Khan), a cartoonist, and Rhea Prakash (Rani Mukerji). The two meet on a flight from Delhi to New York, and due to the circumstances, they end up hating each other. However, they continue to bump into each other. Three years later, Karan helps his mom to plan a wedding and finds out Rhea is marrying Sameer (Abhishek Bachchan). Years later, while visiting Paris, Karan again runs into Rhea and finds out about Sameer's death in a car accident. Karan, along with Rhea’s mother Bobby (Kirron Kher), plans to set Rhea up with one of his friends. However, things didn't go the way he planned. Much later, Rhea and Karan realize that they have fallen in love with each other, and somehow because of fate they keep running into each other. Will destiny play its cards and help the lovers finally unite?