Hum Tum was loosely inspired by When Harry Met Sally... following the encounters of the two main characters until they, after several years and various meetings, become friends and finally fall in love at the end of the movie.
Karan is a cartoonist at one of India's leading newspapers with a daily column called Hum Tum. He calls it that because that's how he sees the world divided: No countries, no religions, just two divisions--boys and girls. When Karan first meets Rhea they disagree on everything, furthering his beliefs, so to put things right he innocently gives her a kiss.
Six months later the duo meet once again and Rhea hasn't forgotten the kiss. Forward ten years since their first encounter, Rhea and Karan become friends again despite their differences, but this time destiny has bigger plans for the pair.