TV pilot production is an inexact science. Certain characters or ideas don't quite click, so you change them, or you abandon them, and then you move on. In these days of leaner budgets, though, it's trickier to deal with the changes as thoroughly as might be ideal, which is why much of NBC's press tour session for "Constantine" was devoted to a character who now won't be in the show past the pilot.

In the original version of the pilot — based on the John Constantine character from DC Comics, here played by Matt Ryan as an exorcist and "dabbler in the dark arts" — Constantine befriends Liv Aberdine, played by Lucy Griffiths, the daughter of a friend of his, and someone with her own undiscovered connection to the world of the occult. The pilot takes Lucy on an emotional journey from skeptical, to fearful, to believing devoutly in the war against evil that John is fighting, and therefore to being his new protege.

After the pilot was shot, though, producers Daniel Cerone and David Goyer (the latter a producer and/or co-screenwriter on all of the recent Batman and Superman films) recognized that Liv, whom they had created themselves, was, as Cerone put it, "Always going to be reactive."

"We felt a bit hamstrung by her, frankly," he admitted.

So one of the pilot's closing scenes will be reshot to explain why Liv is no longer joining John on his supernatural road trip, and in later episodes, the show will introduce Zed, a psychic from the comics who will be played by telenovela star  Angélica Celaya (pictured above).

"
She's just someone who can go toe to toe with John," Cerone explained. "We needed a more dynamic relationship rather than someone who was always a teacher and someone a student."

All of which is fine and good, and Griffiths is easily the weakest link in the "Constantine" pilot, which otherwise does the best that it can(*) to be a more faithful adaptation of the long-running(**) character than the Keanu Reeves movie of the same name. (As Goyer puts it, "We were determined to make John British and blonde and have some scruff," and they even dyed Ryan's hair accordingly.)

(*) One area in which the adaptation butts up against the realities of network TV: comic book Constantine is a chain smoker, and one of his most acclaimed stories ever (the Garth Ennis-penned "Dangerous Habits" arc of the "Hellblazer" comic) involves him contracting terminal lung cancer, but NBC can't let them show him smoking on-camera. So in one scene in the pilot, we see him stubbing out a cigarette at a bar, but that's it. The producers said that their Constantine is a smoker, but that they won't be "glorifying it" — i.e., showing it at all.   

(**) As a teenager, Goyer actually had a letter published in one of Constantine's earliest appearances in Alan Moore's run on "Saga of the Swamp Thing." It was during a period when Constantine was trying to help Swamp Thing fight a rising tide of darkness and evil, and the letter was theorizing what might be behind it. "Ironically," he said, "that's our first season arc."

But the pilot is built entirely around the developing relationship between John and Liv, and her role in whatever war is to come between Heaven and Hell. If people like the pilot, part of the reason will likely be that relationship, and now the show is just changing course abruptly. So why not reshoot it?

"We decided we didn't need to," said Goyer, denying that it was a budgetary issue, even though recent pilots have been plagued by this very issue. (See also "New Girl" being unable to reshoot Damon Wayans Jr's scenes in its pilot with Lamorne Morris, creating problems for several seasons to come.) "One of the hallmarks of John is his friends drop like flies."

If fans of the comics, and/or of supernatural dramas like, well, "Supernatural," embrace "Constantine" in the long run, then Griffiths' briefer-than-planned stint won't be any more of a blot on its legacy than Moira Kelly's short time on "The West Wing," or Glenn Quinn's on "Angel."

But the panel was at least an interesting window into the very imprecise art of making and selling a pilot and then figuring out how it works as an ongoing series.