Karen Effiel is an author writing her latest novel about an isolated man named Harold Crick. What she doesn't know is that her fictionalized character is real. The real Harold Crick is an IRS agent who has lived a dull existence and one day begins to hear Karen's voice as she narrates what she puts on paper to what Harold has and is doing. Because of this Harold insists the help of a literary professor to find out what is happening and ends up changing things about his life including beginning a relationship with his IRS client, a government-hating bakery owner named Ana Pascal. Harold, however, finds trouble when he hears that Karen plans to kill him.
