Rosie Dunne and Alex Stewart are long time best friends. On her eighteenth birthday they kiss even though she was drunk and doesn't really remember it. Not remembering they have kissed, Rosie gives a go at Alex asking another girl Bethany to the prom dance while Rosie herself goes with Greg. Rosie and Greg have a one night stand resulting in her getting pregnant, halting her dreams of studying in Boston with Alex. Alex goes on to Boston with Rosie not telling him about the pregnancy. One day Alex asks Rosie to visit him in Boston. Rosie goes there but at the end leaves angrily because she thinks Alex is using her as a distraction from his own life, including his forthcoming child with his girlfriend Sally. A few years later Greg walks back into Rosie's life and she gives him a chance, so they get married. Alex learns about the marriage but he also separates from Sally due to Sally having an affair.Alex reaches out to Rosie asking if she's happy with Greg, but his mail is intercepted by Greg.
One day Bethany, now a successful model, comes to the hotel where Rosie works. When Bethany says she's going to Boston next, Rosie politely mentions that Alex is there. Rosie finds out that Greg is cheating on her so she divorces him. She finds Alex's letter and contacts him, only to find Alex and Bethany are getting married. Her best friend Ruby convinces Rosie that Alex is the right man for her and that she must fight for him. So Rosie, Ruby, Rosie's daughter Katie, and Katie's best friend Toby race to the wedding. They arrive just after the ceremony. In her speech at the party Rosie admits her love for Alex, though she then covers it with other words. She leaves when the dance starts. Toby and Katie dance, and he kisses her. Katie runs from Toby and Rosie and Alex give chase. Alex says to Katie that Toby is right for her but she says that it feels strange, just like Rosie and Alex never hook up. Rosie agrees with her but Alex reveals the truth about their drunk eighteenth birthday kiss. Rosie goes back home, buys a country house and turns it into a seaside hotel. Alex comes to her saying that Bethany isn't right for him.