The story of Noah is well known and the movie takes it as its basis, but branches out from there. The major issues in the story, besides the ark, is the issue of original sin and its consequences on mankind. Noah, descendent of Able, loses his father to the men of Cain, which makes him the only just man among Cain's spawn. God is determined to kill the unjust, so the rain and the ark. Now, Noah is faced with the impossible task of he and his family constructing an enormous boat. How he does this and how God guides them is only part of the story. Many changes are introduced to the tale. A major difference is the addition of the guardians, fallen angels who were drawn to men and human life.
Very central to the story is his family, how they deal with this mission and a father and husband listening to the will of the Lord. They struggle for it is a will they can not comprehend. Many questions are also addressed, such as where Noah's sons find wives and how they calm all those animals, again stepping away from the Bible for the answers.