Half Girlfriend follows the story of Madhav Jha, a boy from a small village in Bihar, India. Madhav is from a rural background and speaks Bhojpuri, but he dreams of making it big. He is passionate about basketball, which becomes his ticket to studying at the prestigious St. Stephen’s College in New Delhi.

At St. Stephen’s, Madhav meets Riya Somani, a rich, beautiful girl from Delhi who also joins the college through the sports program. Riya is well-educated and speaks English fluently, which is in contrast to Madhav’s struggle with the language. They bond over basketball and become friends.

Madhav falls deeply in love with Riya and wants their relationship to move beyond friendship. However, Riya is not interested in a serious relationship and rejects Madhav’s advances. She only wants to be friends, and Madhav is hurt by this.

Despite her rejection, Madhav cannot move on. He becomes more frustrated and tries to push Riya into a physical relationship, which offends her deeply. Riya decides to end their friendship and tells Madhav not to contact her again.

A year later, Riya marries Rohan Chandak, her childhood friend, and moves to London with him. Madhav, devastated by Riya’s marriage, returns to his village, Dumraon, and helps his mother, Rani Sahiba, who runs a local school. The school is in poor condition, with no proper classrooms or toilets, and Madhav wants to improve it.

To get funding for the school, Madhav learns about Bill Gates visiting schools in Bihar and tries to get an appointment to ask for financial help. To make a good impression, he needs to prepare a speech in English. Madhav turns to Riya for help with the speech. Although Riya is now living in London, she agrees to help him.

While working together on the speech, Madhav and Riya reconnect, and Madhav learns that Riya has been through a lot since their last meeting. After the successful fundraising event, Riya leaves Madhav a letter revealing that she is terminally ill with lung cancer and has only a few months left to live. The letter expresses her love for Madhav, despite her illness.

Madhav is heartbroken and searches for Riya in London to say goodbye. However, he finds out that Riya has disappeared and cut off all contact with India.

Three years later, Madhav discovers through Riya’s journals that she faked her cancer diagnosis. She was not actually ill but had wanted to get away from her past. Madhav, determined to find her, goes to New York and spends three months searching for her.

Finally, Madhav finds Riya at a café in New York called Cafe Wha. They reunite and reconcile, and their relationship deepens. They finally express their love for each other and consummate their relationship.

The story concludes with a time jump of three and a half years. Madhav and Riya are now living in Dumraon, running the school together. They have a son named Shyam and are successfully managing both their family and the school. The novel ends with the author, Chetan Bhagat, visiting the school and seeing how Madhav and Riya have built a life together.