Uh oh. Penny Johnson Jerald is not playing around on ABC's "Castle," returning Sept. 19.

*Things ended quite violently on the season finale of ABC’s “Castle.”

The show follows mystery novelist Richard Castle (Nathan Fillion) as he shadows NYPD Detective Kate Beckett (Stana Katic)  - the model for the main character of his next book series starring “Nikki Heat.”

In Monday’s fourth season premiere, Beckett is fighting for her life after being shot, Castle is plagued by guilt over his role in the events, and the precinct has to deal with an uncompromising new female captain who takes no mess and demands to be called “Sir.”

“You don’t think that name explains itself?” laughs actress Penny Johnson Jerald, who joins the cast this season as Captain Victoria “Iron” Gates. “You don’t call me ‘ma’am,’ you call me ‘sir,’ and ‘iron’ because she’s by the book and nothing will get past her.”

A former internal affairs officer, Gates is more interested in impressing her higher-ups than doing actual police work.  Needless to say, Castle’s constant meddling in police business – all under the guise of research for his novel – will not go over well once she sits behind the desk.

“Hopefully it plays out to be great television because there’ll be contention between the two of them,” says Jerald, 50, from Baltimore. “She is not like her predecessor. He had that paternal flair about him and was nurturing and warm. She’s a bit different.  It’s more of a tough love, if love is in the equation at all.”

In the bonus audio below, Jerald admits she didn’t exactly watch “Castle” before being cast in the show, which also stars Tamala Jones and Ruben Santiago-Hudson.

Castle’s Penny Johnson Jerald on catching up before joining the cast by CherieNic