To a television network executive, the pitch sounds irresistible. "Dark but fantastical cop drama about a world in which characters inspired by Grimm's Fairy Tales exist."

This idea for a TV show has the ingredients the industry is seeking this year: a comfortable set-up (the cop show) with a slight twist (fairy tales). It beat out about 500 other pitches. Then it survived months of second guessing, rewriting, and testing with focus groups. "Grimm" is one NBC is considering adding to its fall prime-time lineup.

Network...