Plot

Dev Saran (Shah Rukh Khan) is a successful soccer player in the United States. He lives in New York with his wife Rhea (Preity Zinta), a fashion designer, his young son Arjun, and his mother Kamaljeet (Kirron Kher).

Maya (Rani Mukerji) is an orphan who is to marry her closest childhood friend Rishi Talwar (Abhishek Bachchan). The two have been raised by Rishi's fun-loving, wealthy womanizing father, Samarjit a.k.a. Sam (Amitabh Bachchan). Dev encounters Maya moments before she is to marry Rishi, and the two have a deep conversation. Although Dev and Maya are strangers, they connect instantly. When Dev bids Maya goodbye, she tells him they should never say goodbye because they may meet again. Moments after they part, Dev is hit by a car and permanently injures his leg; as a result, he is no longer able to play soccer.

Four years later: Dev is now extremely bitter - first because of his inability to play soccer and second because Rhea is very successful in her career, making Dev feel inferior. Dev is now the soccer coach for a team of juniors, including his son, but is frustrated when Arjun doesn't play like him. Maya is in a similar situation: she has found that she is infertile and does not feel any love towards Rishi because she believes he is selfish.

Dev and Maya meet again, and Rhea and Rishi strike up a professional friendship. When Dev and Maya witness Sam and Kamaljeet embracing, they confront them about it. Sam and Kamaljeet explain that having both lost their spouses, they understand each other and have decided to help one another through their loneliness by means of friendship.

Dev and Maya notice each other's marriages failing miserably and, taking into account what Sam and Kamaljeet said, they decide that they need to help each other save their marriages. They meet every day for coffee and discuss their situations. Eventually, Dev and Maya decide to take a break from the stress of their relationships and spend some quality time together. In doing so, they find themselves drawn to one another. They try to give each other ideas to salvage their marriages, all of which comically fail. Dev and Maya realize they have feelings for one another and not toward their partners and feel drawn towards one another.

After celebrating their wedding anniversaries, both couples have an argument. Rhea mentions that she has received a promotion, and Dev goes into a rant, sneering that she is trying to show off. Hurt, Rhea accuses Dev of being jealous of her professional success and makes him realize his failure to be a good husband and a good father because he cannot come out of his bitterness. At the same time, Rishi expresses his frustration at Maya's lack of affection and his resentment toward her inability to have children.

Upset, Maya arrives at the train station and finds Dev, who finally confesses that he has fallen in love with Maya, and so has she. Rhea and Rishi talk with each other and realize they need to stop arguing with their spouses and reach out to them. For a while, both marriages seem to be fine; however, Dev and Maya begin an affair, as they are happier with each other. The two couples attend a ballet show, where Dev and Maya try making each other jealous by showing affection to their partners. The next day, they realize what they are doing is wrong but nevertheless give in to their love and sleep together.

Sam invites the Sarans to dinner to celebrate Kamaljeet's birthday. Here, Dev 'jokingly' admits he loves Maya; Sam is the only one who realizes that Dev was being serious. Shortly afterward, Dev and Maya are caught together by Sam and Kamaljeet.

Sam has a heart attack; on his deathbed, he advises Maya to leave Rishi, as neither of them is happy in the relationship and never will be. After Sam's death, Dev and Maya decide they must end their relationship and go back to their respective spouses but must tell them the truth first about their extramarital affair because neither of them will be able to move on in the shadow of lies. Shocked and heart-broken, Rhea and Rishi decide they have had enough and divorce their spouses. Kamal, fearing that Rhea might separate her from Arjun, requests Rhea to let her live in their house after the divorce, to which Rhea reacts with a teary embrace. Dev and Maya lie to each other and say that everything is fine, believing they'll never meet again, and Maya moves to Philadelphia.

Three years later: Dev and Maya now live alone miserably and have not seen each other. Rishi visits Maya and says that he has fallen in love again and is remarrying, and wants Maya to be his best man, to which she agrees. Rhea attends with her boss Jai (Arjun Rampal), whom she is now dating, and is revealed to be a friend of Rishi's second wife, Catherine.

Rhea confronts Maya about the affair and reveals that she left Dev - Rishi learns the same about Dev and Rhea. Maya is encouraged by Rishi and Rhea to go to Dev, who is leaving for Toronto by train, as they have both moved on and believe Maya should find her true love.

At the station, Dev sees Maya but tries to avoid her, believing she is still with Rishi. However, Maya finds him just as the train leaves. As the train pulls away, the two lock eyes. Seeing her tears, Dev pulls the emergency stop and arrives back at the station. He learns that Maya has also been divorced and alone in these three years.

They finally find happiness with their love and decide to start a new life together. Dev reveals that although he and Maya found happiness together after many years, they sometimes wish that they did not have to cause heartbreaks along the way.