Harold Crick (Will Ferrell) works for the Internal Revenue Service and lives a markedly routine and boring life. That is, until he audits Ana Pascal, a baker. The two like each other, and a romance begins. Surprisingly, that same day, Crick starts hearing the mysterious voice of a woman narrating his life. It doesn't take him long to realize that he is the only one that can hear it. When Harold's watch stops working soon after, he asks someone on the street to tell him the time as the strange voice says, "little did he know that this simple, seemingly innocuous act would result in his imminent death". Naturally, this news startles Harold and he tries to find some answers to the mystery of the disembodied voice. He consults with Jules Hilbert, a renowned literary professor. Hilbert tells Harold to first determine what the voice is doing, if it is some kind of story, what that story is about, and to what genre it belongs.
Determined to turn his life into a comedy rather than a tragedy, Crick visits Ana's bakery and they get a little closer, but Ana gets angry when Harold doesn't accept the cookies that she made for him. Jules suggests that Harold stay home one day and do nothing, and see if there are external forces working on his life. While innocently sitting in his apartment, the building shakes, and Harold finds that it has been partly demolished by a wrecking crew, who were under the impression that the building was empty. With no other choice than to embrace life, Harold tries to do more interesting things and live a more fulfilling life. He takes a vacation, purchases a guitar, and gets closer to Ana. Things seem to be getting better for Harold.
Harold reports back to Jules that his story is most likely a happy one, a comedy. He thinks he might be in the clear until, while watching television, he sees an interview with Karen Eiffel, who has the same voice as the strange narrator. Jules tells Harold that Eiffel is famous for killing off her main characters in ingenious ways.
Frantically, Harold gets in touch with the reclusive Karen and tells her that he is experiencing everything that she writes. She is terrified to hear that she actually has control over someone else's life. She has not yet finished the book, and has not written Harold's death. After giving it some thought and reading the manuscript, Harold tells Karen that she can kill him if she wants, because she is such a wonderful writer.
One day, Harold is on his way to work and he sees a child on a bike accidentally skidding into the street as a bus speeds towards them. Harold leaps into the road, pushing the child out of the way and getting hit himself. While it seems like Harold might die, his wristwatch gets lodged in a part of his body that might otherwise bleed out, and he is saved.
