Michael Cudlitz, Lucy Liu Michael Cudlitz, Lucy Liu

Things will look a little different this season on Southland.

The fourth season premiere (Tuesday, 10/9c, TNT) picks up six months later, and the partnership deck has definitely been reshuffled. Officer John Cooper (Michael Cudlitz), fresh off of back surgery and a rehab stint for painkiller addiction, is now partnered with Jessica Tang (guest star Lucy Liu), a seasoned cop with her own checkered past and emotional baggage. As first teased in the Season 3 epilogue, Sammy Bryant (Shawn Hatosy) and Ben Sherman (Ben McKenzie) remain partnered, and Detective Lydia Adams (Regina King) is training rookie Ruben Robinson (Dorian Missick), an ex-Marine turned homicide investigator.

Get more scoop on your favorite shows in our Winter TV preview

So, what kind of drama can you expect from the new partnerships? We chatted with the cast, who helped us break it down.Officers John Cooper and Jessica Tang

If you're shocked to see Liu in beat-cop blues, you're not alone. "I was surprised by it because I really thought it was going to be something much more in plain clothes," Liu says. "It's been a lot more challenging to be a police officer. ... It put me in a place where I had to really push myself."As Officer Jessica "Pootie" Tang, Liu is somewhat responsible for babysitting Cooper during his first days back on active duty. But because of Tang's own huge mistake (the video of which has circulated the LAPD), she puts herself and Cooper on equal footing. "He's not training her and she's not training him," Liu says. "She's there to keep an eye on him but they have a very similar outlook on what they're doing and how they go about doing it. ... They're really trying to figure something out for themselves. The emotional undercurrents for both of them are there but they don't talk about it, which I think is kind of wonderful."

Check out our list of TV's sexiest crime fighters!

As for Cooper, he's got no problem letting Tang take charge — even if that means letting her drive. "I think he's happy to sort of hand it over for a little while," Cudlitz says. "He wants nothing more than to be back on the streets, and he knows he f----- up big time. To think that he's going to get back everything he had prior immediately is ridiculous. So, he's okay with that. He just wants to be out there doing his job and settling back in."Officers Sammy Bryant and Ben Sherman

After six months of riding together, it's clear this partnership makes sense. Hatosy, whose character gave up being a detective in the gangs unit to return to patrol last season, credits the union's strength to the similarly emotional way the two officers approach their work."Sammy is an emotional and volatile character," Hatosy says. "As a detective, there are procedures and there's a lot of structure and paperwork, and you kind of have to investigate and interrogate and get to the bottom of it. But as a guy on the street, if he sees somebody do something bad, he gets to chase them. And if they hit, he can hit back. It's a bit of a release, and I think that Sammy is confident and comfortable in his skin, more so than we've ever seen him."

Southland scoop: Lou Diamond Phillips to guest-star

However, a case in the Season 4 premiere may divide the partners. When Ben butts heads with a cynical veteran cop (guest star Lou Diamond Phillips) over what's proper police procedure, Sammy is stuck in the middle. But despite his methods, Phillips' character eventually proves himself to be the kind of cop who should be admired by making a life-changing choice that forces Sammy and Ben to consider the weight of the badge."I think that Sammy would like to think that's the kind of cop he is, but I don't think that there's a doubt in Ben," Hatosy says. "He's the perfect hero. There's no way that he's going to shake or he's going to miss the shot. He's going to hit the target every time."Detectives Lydia Adams and Ruben Robinson

Partner change is nothing new for Lydia, but for the first time, she's the training officer, and therefore the dominant figure. "The dynamic that Lydia and Robinson have brings out some of the playful side that I don't think we have seen before," King says. But life at home is, as usual, far from playful, as Lydia continues to struggle with being a single woman. The fact that Ruben is happily married will shed new light on Lydia's relationship woes. "She knows nothing about a family that is together and happy because she didn't grow up in that kind of family," King says. "When you have a single person and married person together, I think the conversation is a little more informative for each person. He's given her insight into what family life may be."And as usual, Lydia will let her heart get the best of her in the premiere, as she tries to keep an informant out of harm's way. "Lydia has always been a compassionate detective, probably to a flaw," King says. "You see how that compassion plays a part in she feels about herself."Southland premieres Tuesday at 10/9c on TNT.