Ally Walker, Sons of Anarchy

WARNING: The following story contains spoilers about the Season 3 finale of Sons of Anarchy. Read at your own risk.

It was a partnership doomed to fail.

On Sons of Anarchy, there was a certain inevitability to how this season's unholy alliance between Jax (Charlie Hunnam) and Agent Stahl (Ally Walker) would end: with one person or the other dead.

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And, well, Jax is the star of the show.

"Once Stahl and Jax were in business, it was kind of over, and I knew that," Walker tells TVGuide.com, noting that she knew creator Kurt Sutter was leaning toward killing off Stahl before Season 3 began. "She's such a bad, bad person that it's really hard to go anywhere else with her."

Stahl, who cut a deal with Jax to clear his mother's name and reduce the club's jail time for pending weapons charges, met her fate by overplaying her hand. Once Jax delivered on his end of the bargain — turning over Jimmy O'Phelan (Titus Welliver) to Stahl's team — Stahl double-crossed Jax by revealing to the club that he had been working for her all along.

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What she didn't count on was that Jax was working a long con that ended with his non-jailbound brothers taking Stahl out. "I think she was worried about it," Walker says. "Jax had proven how smart he was to her in the interview in the jail in Season 2.  So, she was aware of his intelligence, and I think she was aware he could turn on her. She just couldn't see how. I think she figured in the end that he would do anything to get his mother off the hook, and that's what she was banking on."

But even before the double cross, Stahl was doomed in Sutter's eyes. "The thing I wanted to explore with her ... was just the idea that when you have that sort of obsessive personality and need to succeed, ultimately the pursuit of this big prize creates the alpha-cop paradox," he says. "In pursuit of the bad guy, you ultimately become more evil than the evil that you're pursuing. I don't think it's uncommon for that to happen in the world of law enforcement and that's what happened to Stahl. Ultimately, she just became incredibly evil."

The evil streak was showcased in the Season 2 finale when Stahl shot and killed an informant, then framed Jax's mother, Gemma (Katey Sagal), for the murder. It returned in Season 3's penultimate episode, as Stahl killed her own girlfriend to protect a new set of lies Stahl had created to exonerate Gemma based on her deal with Jax.

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"When you have a character cross that line and do what she did, logically it's really hard to continue without being too absurd," Sutter says. "I think once she kills someone like that, at that point the danger level is so high that, whether or not it was in Jax's plan to begin with, she would ultimately have to go away."

Sutter says he also learned a lesson from the Season 2 finale, when he let his antagonist, Ethan Zobelle (Adam Arkin), get away relatively unscathed.

"Guys like Zobelle get away — they're almost above the law. And I think that was a very unsatisfying ending for people," Sutter says. "This season, it was organic that Stahl crossed a line and she would pay the price and therefore it was organic that she would die."

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"The bad guy must go down," Walker adds. "Maybe she was on the side of right, but who she was as a human being was very vile. Ultimately, human beings create their own destiny, and I believe June definitely created hers."

But don't worry: Walker may soon live again on your TV screen. She's preparing to shoot a pilot for Lifetime called Exit 19, in which she plays a quirky homicide cop.

"I think strong women usually get relegated to being cops or doctors," Walker says with a laugh, noting her string of law enforcement roles. But her new character is funny. "[The show] is much lighter than Sons, and for me it's good to get back to doing some comedy again. ... It's not completely about violence and darkness."

What did you think of the Sons of Anarchy finale?

Check back later for more Sons of Anarchy scoop from Kurt Sutter, including what's ahead in Season 4.