Yeh Unn Dinon Ki Baat Hai

Set in Ahmedabad in the 90s, Naina Agarwal is a 16-year old girl studying at Pragati Vidya Mandir. She has a joint family and lost her mother. Sameer Maheshwari, a 17-year-old hosteler lives in Nainital and gets suspended from his school due to his mischievous behaviour. He returns to his maternal grandfather in Ahmedabad. As his father is dead, his mother Vishakha had married Vivek Somani and lives in Delhi. He hates Sameer. Sameer joins Naina's school as her classmate; instantly she falls for him.

Although Naina has a soft corner for Sameer, she had to stand against him on various instances, because she is the Head Discipline Monitor of her school. Naina's father who is the librarian of that school also stands against Sameer and insults him. An enraged Sameer decides to take revenge on Naina, by engaging in a bet to his seniors, wherein Sameer has to make Naina say "I Love You" and hug him. Sameer starts wooing Naina.

After a few months, the school decides to go on a trip to Mount Abu. Sameer and his friends Munna and Pandit decide to complete their bet during the trip. During their trip, Sameer realizes that Naina is very caring and good at heart. Though Sameer has a soft corner for Naina, he never realizes that he has already fallen for her. On the last day of their trip, Naina finally confesses her feelings. She soon learns of the bet and feels dejected and heartbroken.

After a few days, Sameer finally realizes his feelings for Naina; he tells his friends about this. Sameer is now clueless about what to do now, as Naina hates him now. Meanwhile, Arjun gets to know about the bet. Enraged, he confronts Sameer and Sameer pushes Arjun, and the latter breaks his leg. This causes the growth of hatred in Arjun and Sameer. As a punishment, Sameer is asked to serve Arjun until he recovers. During this time, Pooja's marriage is fixed. Sameer apologizes to Naina who finally forgives him.

Sameer's grandfather passes away and he has to shift to Delhi, which Naina discovers days later. There Sameer bonds up with his stepbrother Rohan and half-sister Deepika. Sameer and Naina both communicate through phones and letters. This makes their relationship stronger.

Sameer returns to Ahmedabad after a year. Naina, Sameer, and their friends enrol in VJN College. In college too, they face too many challenges due to their nemesis, but their love gets stronger day by day. Naina also breaks up with Sameer due to Arjun-Shefali's relationship to be exposed to their families.

One day, Beena fixes Naina's marriage to an arrogant CA Sharad. The alliance soon breaks because of Sharad's violent behaviour towards Anand and also for slapping Naina in front of the college. During this time, Anand gets to know about Sameer and Naina's relationship and he approves, because of Sameer's true love. Anand also promises to conduct their marriage.

After a lot of trials and tribulations, the couple finally gets married. Sameer had built a huge bungalow for Naina with the money Nanu gave him. In the meantime, Swati marries a businessman, Preeti marries Shubham, Munna marries Rewa and Arjun marries Juhi.

Sameer's Mamaji and his son keep an eye on Sameer's grandfather's factory and business. To kick out Sameer from the business, they insult him in various ways. Enraged Sameer returns home. Hot-headed, he and Naina have a major fight, the latter knowing nothing about what happened in the factory. Both of them slap each other and Naina returns to her home. She soon gets to know the incident and goes to meet Sameer; she meets with an accident. This reunites the couple.

Sameer and Naina start their own business, called 'Samaina boutique' which doesn't go very well. Sameer gets to act in an advertisement, where he realizes his acting potential. They decide to travel to Mumbai for an acting career. They decide to sell their house. They also consummate their marriage.

The couple travel to Mumbai with Rakesh. Naina finds a job as a writer, but due to her boss's negative attitude, she resigns. Sameer gets his first acting venture in a pressure cooker advertisement but struggles to find a permanent job. He decides to support his wife with writing. They present their first story to Aruna Irani. She accepts their story and telecasts their serial.

Finally, Naina and Preeti are pregnant. Naina delivers a baby girl and Preeti delivers a baby boy. Sameer and Naina name their child Suman Maheshwari. After the birth of their child, they buy their rented house in Mumbai. Sameer also buys his Ahmedabad bungalow which he sold while travelling to Mumbai. After 2 years, they return to Ahmedabad and reconcile with their family members, who turned foes during their marriage. Naina, Sameer, Munna, Swati, Pandit, Preeti, Hema, and Kamya reunite at their school's 50th anniversary. Sameer and Naina reminiscence their old days. The couple lives happily ever after. The story ends happily in 1998.