Evan Baxter, played by Steve Carell, is a newly elected congressman who moves to a suburb of Washington D.C. with his wife Joan, played by Lauren Graham, and their three children. Evan has made a promise to his constituents to "change the world", but his focus on work causes him to neglect his family.
One day, while getting ready for work, Evan begins to grow an unusual amount of hair and is visited by God, played by Morgan Freeman. God tells Evan that he has been chosen to build an ark, just like Noah did in the Bible, as a way to prepare for a flood that will soon occur.
Initially, Evan is skeptical and dismisses God's request, but he soon realizes that he cannot control the strange occurrences happening around him. He begins to build the ark in his front yard, which causes his neighbors to think he's insane and leads to rampant media coverage.
As Evan struggles to balance his personal and professional life, he also faces opposition from Congressman Chuck Long, played by John Goodman, who views him as a threat to his own political power. Eventually, Evan's family and even some of his colleagues and neighbors join him in his mission to build the ark.
In the end, the flood does indeed come, and Evan and his family are saved by the ark. Evan learns that his desire to change the world should not come at the expense of his family and that small acts of kindness can have a big impact. The film ultimately promotes the importance of environmental responsibility and caring for others.