Sophie (Drew Barrymore) and Alex (Hugh Grant) successfully write a song for pop star Cora Corman to record, thus securing a comeback of some kind for aging rock star Alex. However, Sophie objects to Cora's lack of artistic integrity and when Alex is unwilling to stand up for Sophie, their romance falters. Sophie faxes over the additional lyrics Cora has demanded: putting into words her mistrust of Alex's feelings for her.
When Sophie goes to the performance to hear her song sung, Alex first sings a love song penned to her, apologizing. Then Cora and Alex perform the duet Sophie helped co-author and they sing it as Sophie and Alex intended, and not as Cora had suggested earlier - as a backdrop for her to dance (turns out Cora is a mushy romantic and when Alex told her that performing the song this way would help him win back Sophie, she agreed). All is well, and Sophie and Alex reunite. Sophie becomes a successful lyric writer and Alex has a second wind in his career.
Thanks Mary C!