Dr. Mrinalini 'Mili' Chakravarti (Sonam Kapoor) is a physiotherapist who works for the IPL. Her mother Manju (Kirron Kher) hopes that she will find a man someday, stating that it will be even better if he belongs to royalty. As fate would have it, her services are called for by a royal family whose king's legs are failing him.
Mili travels to the Sambhalgarh palace and meets the rigid queen, Nirmala Devi Rathore (Ratna Pathak), who is not amused by Mili's enthusiasm and clumsiness. Mili finds that her casual way of living does not appeal to the royal family whose strict disciplinary rules demand otherwise. She meets Yuvraj Vikram Singh Rathore (Fawad Khan), the prince, whose distant personality makes him similar to his parents. Mili also discovers that Divya, the youngest child of the family, has an interest in acting and is planning to run away from home. Mili befriends Divya and tries to convince her to not run away.
The king keeps avoiding his exercise and this troubles Mili because she is determined to cure him, so she turns to Vikram for help. He gives Mili the same answer that the queen gave her, "if she cannot handle the job, she may leave". Mili gets furious and accuses the royal family of being stubborn, rigid and self-centered. Vikram reconsiders, but the king refuses. Just when Mili is deciding to leave, she learns the reason for the king's unwillingness to be cured from the royal servant Ram Sevak. Ten years ago, Ambar, the family's eldest son, died in a car crash. The king had gifted a sports convertible to him and the two went for a ride. Ambar lost control of the car due to over-speeding and died, and the King's legs became disabled and he went into a coma for six months. Since then, the queen changed. The Palace used to be fun and everyone would throw parties and laugh but after the accident, everybody changed.
Mili shames the king into getting over his guilt and forces him to perform his exercises. Mili tries to befriend the king by making him tell her about wine and play video games; she speaks to the king about the 10 year old accident with Amber and persuades him to exercise. Once the king persuades the prince to take Mili with him to Surajgarh Palace. After that, the prince leaves Mili in the market and goes to a meeting. Mili gets kidnapped, and when Vikram saves her, they both kiss.
The next day, they both decide to forget about it but the two start falling for each other. Mili confesses her love for him but Vikram refuses to acknowledge it, saying that they come from two different stocks. He is also engaged to a lady of his status Kiara (Aditi Rao Hydari). Divya runs away to try out for auditions in Jaipur. Mili informs the queen that she knew about Divya's plans. The queen becomes furious and Mili is ordered to leave. Divya returns and tells Nirmala that she came back because of Mili. The king surprises Nirmala by standing up from his wheelchair and admits that he saw Divya run away. He tells her that this is what Mili has been trying to teach them; to love life as it is. Mili, however, is heartbroken due to Vikram's refusal. Vikram breaks off his engagement with Kiara and confesses his love for Mili and the royal couple gives him their blessings, telling him to go find her in Delhi. Vikram finds her house and finds out that Mili is gone for therapy. He goes to the place where she is being treated. Vikram is shocked to see the place. It is actually a paintball arena. Mili agrees to his proposal. She does shoot paintballs on Vikram. Vikram wins Mili's mother's approval by proposing to Mili in her style, and hence, as the wife of Vikram Singh Rathore, Mili is given the title of The Royal Misfit.