Joan of Arcadia follows the Girardis, who have recently moved to the small town of Arcadia from the big city after Will becomes the chief of police. Middle child Joan is unhappy with the move, and her family - including science nerd Luke, paralyzed former jock Kevin, and their perpetually flustered mother Helen - isn't making things easier.
Then, Joan starts speaking to God, who appears in the form of various people giving her assignments to help those around her. As she befriends the zoned out avant garde sculptor Adam Rove and androgynous rebel Grace, Joan continues to follow God's assignments, unsure if she's truly communicating with God or if she's simply losing her mind.