When you're master and commander of your own hit series, you can do anything you like: make a cameo appearance, name a character after yourself, give a job to your daughter, Tori... The sky's the limit! Joan of Arcadia creator Barbara Hall knows this very well. So, she tells TV Guide Online, she refused to play God with the songs she writes and records with partner Michael Guidry as the Enablers.

"A lot of different people pick the music for the show, and what I do is make [our material] available to them, because, for me, it doesn't count unless they choose it," Hall explains. "Otherwise," she adds with a laugh, "it's just me putting my music on my own show, which is not hard to do!"

Finally, after almost a full year, Hall's team of taste-makers has selected one of her tunes, the perkily ponderous "Mystery," for use in Friday's season finale (8 pm/ET on CBS). We can't accuse the staff of kissing up to the boss lady, either: She has a lovely voice, warm and wise, and this deep cut, like the seven tracks on the Enablers' independently-released folk-pop CD, is leavened by brain-teasing wordplay.

"I wrote 'Mystery' specifically for the show," she says. "I thought, 'Well, I should have something in my canon that is in the vein of what we like to use'." Her mission accomplished, viewers can listen for the ballad in "a scene where Joan (Amber Tamblyn) and [her brother] Kevin (Jason Ritter) talk to each other. It's about how you know when you've found your 'thing'... your calling."

With or without more lyrical contributions from Hall, Joan's quest to find her place in the world will continue in the fall. "This last episode is about Joan getting sick and starting to doubt her connection with God," she reveals, adding that the teen's internal debate is the crux of the program — always has been and, as far as she can see, always will be. "The show is about a perception of reality and when to trust it, and the first episode [next season], or at least an episode early on, is going to be an interesting dance between Joan and God.

"Joan's going to feel like a spurned girlfriend or something," she elaborates. "It's like, 'Okay, God, you're going to have to earn your way back [into my good graces].' I think their relationship is going to be very different next year." For the faithful among the audience, the turnabout should feel more truthful than fictitious. "We're always breaking up with Him," Hall concludes, likening the Lord to an old flame who refuses to remain snuffed out. "But you keep running into Him. He really is bigger than us."