Joan Girardi has begun acting a little strange since her family moved to the city of Arcadia. No one knows that various people keep introducing themselves as God, and then giving the teenager specific directions to do things. Unsure of what God wants, and if she's even sane, Joan tentatively begins to follow God's cryptic directives, all the while trying to retain a "normal" teen-aged existence.
Gawky teenager Joan Girardi (Amber Tamblyn), who has recently moved to Arcadia, Maryland with her family, suddenly starts meeting with strangers who claim to be God in human form, and who give her incomprehensible tasks. Each task seems to have "good ripples" (as Joan puts it) and she is willing to undertake more of them, but mysteries remain. Is Joan delusional? Or the victim of a huge practical joke? If she really is dealing with the deity, why did He pick an unpromising girl to do His bidding, and what are His plans for her?
Without committing to any particular religious tradition, the show deals with philosophical issues that few other shows touch. There is also a surprising bit of comedy contrasting Joan's everyday existence with her bewildering visions (After "God" assigns her one task too many, Joan asks "Why don't You assign me to get a boyfriend?") There are strong supporting characters, many with ideals of their own: the unhappy rebel Grace Polk; Joan's science-obsessed brother Luke; her father Chief Girardi, a religious skeptic trying to fight crime and corruption; and the unworldly artist Adam with whom Joan falls in love. Surrounded by such strong-willed, positive people, we are still encouraged to wonder: why Joan?