Timothy Hutton, Gina Bellman
Leverage executive producer Dean Devlin says Season 4 is all about consequences, and few events are likely to have more fallout than the hookup between Nate and Sophie in the Season 3 finale.

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Devlin says the writers considered the "Moonlighting Curse" before agreeing to pair up Nate (Timothy Hutton) and Sophie (Gina Bellman). "It was a big, well-talked-out decision and we were very nervous about the idea," Devlin tells TVGuide.com. "Every season, we've tried to end the season as though it's our last. So we thought if last season was our last, we wanted them to be together. But we also threw in a big "Whoops!" at the end when they realize they're in bed together."

And that "whoops" will drive the early part of Season 4, as Nate and Sophie try to keep the secret from the rest of the team. In the season premiere (Sunday, 9/8c, TNT), Nate goes to great lengths to avoid even talking about it with Sophie. "They certainly want to keep it away from the work ... but it begins to affect the work in an adverse way," Hutton says. "There are eventually some moments of crossover where they have to get a hold of whatever this is and define it. But neither of them want to define it — they think they can get away with it."

But don't count on that. "The other guys are tremendously sharp, so you'll see as the season goes on that we think we got away with a lot more than they actually did," Hutton says.

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Meanwhile, a pair of the snoopy team members — Hardison (Aldis Hodge) and Parker (Beth Riesgraf) — have their own set of unresolved feelings to deal with this season. "Fans are going to be excited," Riesgraf says. "They are going to be rewarded for their patience." Adds Hodge: "There's just a love and respect there for the foundation of the friendship, and there will be something very interesting coming out of that."

But isn't this a show about a bunch of cons busting baddies? "We've gone a lot more emotional this year," Devlin admits. "The fun is still there, the heists are still there, but I think people are going to be surprised about how impactful some of the episodes are. ... [The team's] relationships are going to develop in ways that are profound."

One thing's for sure: The team will have to be tighter than ever to face the next challenge that's coming. Suffice it to say, the tables have turned. "You can't keep taking down the richest, most-powerful people in the world without there being some blowback," Devlin says. "We're going to see a little bit of the darker side of vigilante justice."

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In particular, look for a mysterious man named Mr. Latimer (guest star Leon Rippy) to keep very close tabs on Nate and his team. "We become the hunted," Hutton teases. "We have to work now on two fronts: Help someone in a new case but also watch our back because someone is after us. A very dangerous entity is on our back."

All that added pressure will test each team member in new ways. "The weaknesses in this chain become more evident," Devlin says. "Every character has an Achilles' heel."

And that especially includes Nate, whose drinking problem has always been a concern. "The drinking ... is a symptom of the larger problem: Nate is spinning out," Devlin says. "Nate is a control freak trying to come to grips with the fact that he doesn't have control over much. That's going to become a big problem for him this year. One of the key factors is that someone is outwitting him, and Nate's not used to that."

Season 4 of Leverage premieres Sunday at 9/8c on TNT. Watch our interview with Hutton and Bellman: