Plot

While on holiday, Avi meets Naina and falls in love with her. Smitten, he decides to stay and work in her cafe. He confesses his love in a letter, however it's Naina's mother who mistakenly reads it.

A man under the spell of love decides to stay back and start working at the place he had come down for a vacation. He reverts to sending a letter to the woman he had fallen for, but the woman uses the vagueness of the letter to boost her mother's confidence, making her think she has a secret admirer.

Avinash (Avi) (Rajkummar Rao) is visiting his relatives Kannu Bua (Kiran Juneja) in Shimla on a vacation. Avi is a former translator at Japanese Embassy in India. Avi is really awkward around girls and stammers when it is time to reveal his true feeling to them.

Naina (Rakul Preet Singh) runs a cafe called National Cafe in Shimla and has friend Brownie (Zoya Khan) & Captain Uncle (Shakti Kapoor), who runs the cafe day to day. Naina has a wild temper, and Captain is worried that due to her aggressive attitude, their staff doesn't stay with them for too long. Avi's mom (Nita Mohindra) is on the lookout for a suitable match for Avi and sees Naina one day and wonders if this beautiful girl could become her daughter-in-law. Avi sees Naina one day and falls head over heels in love with her. He gets a job as a odds job man in her cafe. Avi is given a fixed salary of Rs 5000 per month.

Rukmini (Hema Malini) is Naina's mom and still pines for Tilak (Kanwaljit Singh), who was her husband till he abandoned her for a younger girl, with whom he has a live in relationship now. Due to her feelings Rukmini is hesitating to sign the divorce papers and to move on with her life. Rukmini was preparing a feast for Tilak's birthday, but this makes Naina livid, and she throws all the food in garbage. Rukmini is confident that Tilak has strayed before, but eventually he will return to her. Daadi (Kamlesh Gill) is Tilak's mother but stays with Rukmini and Naina.

Naina vows to get Rukmini married to another guy to break social conventions that men can marry again, but women can't. Meanwhile Avi tries to impress Naina by fixing her old decor cafe, a job that had been delayed multiple time by her regular contractor Vikas. Naina befriends Avi and they start spending some time together. Naina is an open and free-spirited person, but Avi mistakes this for her genuine interest in him.

Avi struggles to express his love to Naina verbally, so his friend Jude (Tarun Wadhwa) advises him to express his feelings via a letter. Avi writes Naina a love letter and puts it in her office but doesn't sign his name.

Naina throws the anonymous letter away. Avi is sad to see his letter in a trash can, but then Naina gets a brainwave and asks Avi to retrieve the letter from the trash can, which makes Avi think that Naina is having a change of heart. Naina starts writing love letters to her own mom Rukmini (under an anonymous name, and she copies the first letter written to her and writes it again but this time for Rukmini), so that Rukmini moves on from Tilak in her life.

Meanwhile, Naina gets suspicious about Avi's over-excellence in the job, assuming he is not here to work for her, but to gradually take over the cafe. She fires him, but he says he will stay another month because according to the law, an employer must not fire an employee without noticing him in advance for at least a month.

Rukmini is ecstatic that a stranger has fallen in love with her. She asks random people on the streets if they have written the letter to her, which embarrasses Naina. She signs the divorce papers with Tilak and resumes her training of dance. Meanwhile Avi is not happy to find his letter to Naina in Rukmini's hands. Rukmini waits for the next letter, so to keep her mum's wishes, Naina writes her a letter and asks Avi to deliver it to their home. Rukmini is glad to see Avi delivering the letter and assumes that Avi is the one writing love letters to her. Rukmini confides in Naina, who knows that Avi has no feelings for Rukmini. to handle the situation without hurting her own mom, Naina begs Avi to pretend to love her mom for a few weeks.

Avi is very angry but helps Naina by helping Rukmini make Tilak jealous of his relationship with her. Now Rukmini starts spending time with Avi and Avi's family finds out. They want to meet the girl. So, Avi asks Naina to meet his family as his girlfriend, which she agrees. Avi's family wants to meet Naina's mom to talk about wedding plans. Although Rukmini feels that they are there to ask for her own hand in marriage for Avi.

Avi is so confused that he confesses everything to Captain Uncle. Avi realizes Naina is not interested in him at all, and even gets angry when receiving his love letter and that she just wants to use him to cheer up her mom. Avi decides to leave Shimla as he sees no way out. Rukmini comes to meet Avi at the station and indicates that she knew everything from the beginning and played along as she was also waiting for Naina to fall in love with Avi. Before leaving Avi tells Naina that he wrote the first letter to her.

Some time later, Naina receives wedding invitation from Avi. Shocked Naina immediately visits Avi, and asks him to cancel the wedding and marry her instead. Avi agrees.

It is finally revealed that Avi was not actually going to marry. The wedding invitation is a plan made up with by Rukmini to re-unite the two lovers. Later in Avi and Naina's wedding, Rukmini meets and reconciles with one of her former lover (Dharmendra).