It's tough playing by the rules in Gotham City. The villains certainly don't, and even some of the law enforcement is corrupt. Then there's Jim Gordon (Ben McKenzie), a by-the-books homicide detective who increasingly finds himself crossing the line between right and wrong to maintain order. This fall, the second season of "Gotham" on Fox promises to put Gordon's moral compass to the test with an infestation of old rivals, new enemies and life or death decisions.

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Actor Ben McKenzie spoke with the press during roundtable interviews at Comic-Con International in San Diego about Gordon's tough decisions, his reluctant deal with Oswald Cobblepot (Robin Lord Taylor) and his crazy ex-girlfriend, Barbara (Erin Richards). In addition, McKenzie spoke about Bruce Wayne (David Mazouz) and Gordon's growing bond and newfound allies in their war against crime.

What big changes are in store for Jim Gordon this season?

Ben McKenzie: We pick up Season 2 where it's a reversal of fortune. Young Mr. Cobblepot is the king of Gotham and Mr. Gordon is at the lowest he's ever been. He's been punished by Loeb for saving Falcone's life and foiling Loeb's plan. So, he's a traffic cop and he's pretty bitter about it. As always in Gotham, things change quickly and the rules are reversed, yet again.

Does Oswald Cobblepot still believe they are friends?

Yes, in his own demented way, yes, that's a friendship to him. They are both aware of what the nature of their friendship is. It's a friendship borne out of being able to do favors for each other and being able to get things done for each other. That's the way Gotham works. So, they are friends, but just make sure when you are giving your friend a hug, there's not a knife in your back.

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In what ways will more people come to help him fight against this ongoing corruption?

If Season 1 was the origins of Gotham as a city, that was ruled by crime families, now that we've destroyed that at the end of Season 1 with Maroni being dispatched and Falcone effectively retiring and conceding the throne to Cobblepot, Season 2 starts to explore the rise of the villains. These villains are much more pernicious than the crime families. The crime families actually wanted order. Law and order is actually how you get money out of this situation. But, when the wheels fall off and the true villains arise, it's anarchy. To combat that, there basically has to be an arms race. The good guys have to arm up. We'll get into that later in the season, but the good guys have to arm up.

There's always been a fine line between law and order in Gotham. How do those lines become a little bit blurrier for Jim?

Immediately, in the first episode back, you'll see a deal with Mr. Cobblepot that has extremely negative consequences. Jim has learned he has to do what he has to do to get things done. It's a real change for him to throw morality to the side. He's still serving the greater good in his mind by doing whatever he has to do. It's a little sad to watch that go away, but that is the journey we are going on. What he's learning is how do you get power in Gotham and how do you hold onto that power and how do you dispense that power? You only do that by playing pretty rough.

Does he start to feel Harvey Dent had some valid points?

Yeah, he does. Harvey starts to go, "I didn't mean it that much. Come back."

How will Bruce and Jim's relationship evolve this season? Will we start to see the seeds of that deep friendship Batman and Jim will eventually have?

Yeah, they were on the outs in the middle to the end of the first season. Bruce felt betrayed by Jim for not living up to his promise to solve his parent's murder. They are slowly picking up the pieces. At the same time, Bruce is not being completely honest with Jim. As he discovers this cave his father had, Bruce embarks on his own journey and doesn't tell Jim that he is doing it. The secrets also start to build up as well. They know what they are up against in terms of the bad guys, so they are on the same team, but Bruce isn't entirely honest with him about what he's up to.

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What's on the romantic front for Jim? He has two women in his life.

Yeah, we have a little bit of that, too. Obviously, Barbara has turned from loving partner to psychotic ex-girlfriend. She only gets crazier in Season 2. That puts a strain on Jim's relationship with Thompkins (Morena Baccarin). Thompkins is one of the few people he has to actually confide in and rely upon. But, as she watches Jim turn dark, she starts to question her own belief in the man. Can her own love for him withstand the turn that he's taking and can he pull back? Can she keep him from turning all the way to the dark side?

"Gotham" returns to Fox Monday, September 21 at 8pm EST.