Amber Tamblyn is in a biting mood. The young star of CBS' ''Joan of Arcadia'' just finished shooting her umpteenth scene of the day as a modern-day Joan of Arc, and she's looking to release some tension. So she grabs the arm of costar Jason Ritter -- who plays her wheelchair-bound brother, Kevin -- and chomps playfully. ''Ouch!'' exclaims Ritter (''Freddy vs. Jason'') while examining the reddish dent on his upper arm. ''You left a mark.''
In more ways than one. Proving that 20-year-old breakout stars aren't found only on The WB, Tamblyn has inspired audiences as God's sulky instrument of change, Joan Girardi. The Friday-night drama has surprised critics and execs by dominating its 8 p.m. time slot among young adults, lording over NBC's Alicia Silverstone dramedy -- and ''Joan'''s former time-slot competitor -- ''Miss Match.'' (NBC soon shipped ''Miss'' to 9 p.m. to avoid ''Joan'''s ratings wrath.) ''It's so exciting to me that people are actually enjoying the show as opposed to just blowing it off,'' says Tamblyn, best known for roles in ''The Ring'' and ''General Hospital.'' ''As soon as the word God comes out of your mouth, people are like, 'Uh-oh, it's going to be a 'Touched by an Angel.''''
Hardly -- you won't find Della Reese or a note of ''Angel'''s sappy orchestral music on ''Joan'' (which relies on acts like Patti Scialfa and the White Stripes). Still, ''Angel'''s legacy wasn't far from CBS executives' minds when they developed the series. '''Touched by an Angel' was an industry unto itself,'' says CBS exec Nina Tassler. ''We knew it had an audience. But who was going to tell these stories?'' Enter Barbara Hall, the creator of CBS' ''Judging Amy,'' who started studying religion after surviving a violent crime; she ultimately converted to Catholicism. ''I started thinking, what would it look like if God tried to contact a teenager today? I made the decision that God would have to come to a teenage girl visually,'' Hall says. ''Joan of Arc heard voices, but kids today aren't going to hear voices because you'd have to get the iPods off their heads.''
Adopting various forms, God directs an ambivalent Joan to perform simple tasks that -- through a series of chain reactions -- influence the greater good. Granted, having Joan build a boat in the family's garage doesn't heal Kevin, but it encourages her dad, Arcadia police chief Will Girardi (''The Last Don'''s Joe Mantegna), to bond with his now-distant son as they complete the divinely silly project.
Finding a young actress with the right combination of skepticism (ark building!?) and idealism was a challenge. ''If you don't have the right girl, then you have a 'Muffy Meets God' series,'' says Mantegna, who stars opposite Mary Steenburgen as Joan's mom, Helen. ''This girl's got to come off like a high schooler with the mind of a 50-year-old. I don't think Amber understands how good she is.'' Mantegna has equally laudatory words for Ritter, whose father, John Ritter, died when Joan was shooting its fifth episode. ''People who have been able to see the depth of his father, John -- how he's so much more than Jack Tripper on 'Three's Company' -- shouldn't be surprised to see that Jason's got it as well.''
While the 23-year-old actor prefers not to discuss his father, Ritter offers insight into how he portrays a newly paralyzed young man. ''It's an impossible thing to imagine,'' he explains, ''so I try to think of something that I can never have again. I have to make it real for me.''
One of the most appealing parts of Joan is the producers' desire to keep it real. In the next couple of weeks, God instructs Joan to try out for the cheerleading team (which leads to an episode about teen pregnancy -- don't ask). ''Joan's answering these questions that people who are going through the hardest periods of their life wish they could ask God,'' says Tamblyn. ''It's exciting to be in that position.'' Not that the actress would want that responsibility in real life. ''If people were to come up to me and be like, 'Tell God that I need a new wardrobe or something,' I couldn't do it.'' It's okay, that's why God made ''Queer Eye.''