It's a time of change for the fourth season of In Plain Sight.

Characters are changing. The marshall's office has a new muffin-bearing officer.

And Mary Shannon's pregnancy hasn't even been dealt with yet.

In Plain Sight—about the US Marshall’s highly secretive branch of the witness protection program (WITSEC) which relocates federal witnesses—airs at 10 pm Sundays on the USA Network.

Mystery Scene recently interviewed Mary McCormack, who plays Mary Shannon, and Frederick Weller who plays Marshall Mann. The first installment of the interview ran May 1, 2011.

Here's the second part of that interview.

Half of this season of In Plain Sight already had been shot when McCormack announced she was pregnant in real-life. McCormack and her husband producer Michael Morris are expecting their third child; they have two daughters.

Rather than having her stand behind desks, be seated a lot or wear jackets (in the New Mexico heat!) to try to hide her pregnancy, the writers are making Mary Shannon pregnant, too.

Will this new development make Mary Shannon even grumpier?

“I started out pretty cranky,” said McCormack, with a laugh.

“Yes, she might have been maxed out on crankiness already,” added Weller.

In Plain Sight melds solid plots with character studies each week. The chemistry between McCormack and Weller is a highlight of the series. The two are friends off-camera and McCormack is godmother to Weller’s daughter.

The actors have their own ideas about what keeps viewers returning.

“I think it's a great drama with a sense of humor. And I don't think that's a very common combination on television,” said Weller.

“USA really does characters well," added McCormack. “Even if you weren't interested in the procedural side of our show, or the witness protection side of it, I think the character relationships are really rich and fresh and funny. I love reading the scenes between me and Fred and I love Paul Ben-Victor's character so much.”

The WITSEC background helps, too.

“Witness protection just makes for exciting stories and it's a really rich sort of place to grab stories from,” said McCormack.

“People starting over completely, saying goodbye to their lives before. That never ends in terms of story opportunities.”

And Mary Shannon herself offers endless story opportunities, too.

“The pregnancy obviously is the huge shift around which all other shifts are defined,” said Weller.

“Mary Shannon is a person who doesn't let people in,” said McCormack.

“She barely lets Marshall in and he's the closest person in her life to her. And so to me the pregnancy is an opportunity for the audience to just know the real her. The audience has a really intimate relationship with her, even though she doesn't really allow anyone else to," said McCormack.

”And the stabilization of the family is continuing obviously. [Mary Shannon's sister] Brandi is engaged and getting married. And so far her relationship seems to be going great. And [Mary Shannon's] mother is still sober and doing great, and so that's all confusing for Mary Shannon. But I think in an interesting way.”

Photos: Mary McCormack and Frederick Weller, top; Weller and Paul Ben-Victor; McCormack. USA Network photos