Arguably the most neatly scripted series on television returns this month. And if there’s anything you can say about Season 4 of “Mad Men,” which gets going Sunday on AMC, it’s that anything can happen.

That was the takeaway from Season 3’s end, and it’s what we hear loud and clear from series co-stars John Slattery (who plays Roger Sterling), Vincent Kartheiser (Pete Campbell) and Jared Harris (Lane Pryce).

Last season’s finale was effectively a tabula rasa: Rather than become drones for McCann Erickson, Don, Roger and Bert (Jon Hamm, Slattery, Robert Morse) conspire with Lane to start a new agency – stealing away with Sterling Cooper’s best accounts, talent and resources in a weekend raid. And in the wake of Betty’s (January Jones) discovering Don’s concealed identity, she’s seeking a divorce.

“I think he did an amazingly courageous thing in climbing up the ladder and pulling it up behind him,” Slattery says of series creator Matthew Weiner. “There’s nothing but potential.”

“Potential” by definition implies uncertainty. And with Don, Roger, Bert and the others casting their fates to the wind, we have a lot of it.

As Season 4 opens, what will be different? First, according to Slattery, we may be looking at a two-year jump ahead to 1965. (Weiner has discussed in the past that he would like to take the series through the end of the ’60s, so the leap would make sense.) But the passage of time won’t be the biggest change.

“Everybody has to account for themselves now,” Slattery explains of the vibe at the new agency. “Whereas before it was just, ‘My name’s on the building, so I can do whatever I want,’ now no one can just do what they please – everybody’s responsible for everybody else as well.”

“This is a group of people who are all taking different-sized risks,” Kartheiser adds. “With some of the characters, like Roger Sterling or Don Draper, you get the feeling these guys are doing pretty well. ... But they have a bit of a net, whereas other characters are really risking their finances and their futures.”