Maura Tierney returns to television in the legal drama The Whole Truth. She plays a prosecutor up against Rob Morrow as a defense attorney. Each week, the lawyers will present their cases so the audience can figure out the whole truth.

“I think that’s what’s exciting about it,” Tierney said. “Every week you get to decide whose case you’re liking or whose case you’re believing. Is my case the stronger case or is Rob’s case the stronger case? Unfortunately like in life, on the show justice is not always achieved. The bad guys don’t always get convicted. The good guys don’t always go free. The audience is privy to that, gets to see if we were right or wrong.”

Playing courtroom scenes adds another layer to Tierney’s performance too. Any lawyer has to put on a show for the jury. “That’s true. I was like, ‘How much is this character performing when she’s in the courtroom?’ The first scenes we did were in the courtroom so I didn’t even know where the baseline was. It’s interesting. You’re acting the character and the character’s acting a little bit in front of the jury.”

Legal jargon should be a tad easier for Tierney than ER’s medical lingo. The Whole Truth is also more about the job than the personal drama. “This character is a lot less psychologically clouded and has a lot less psychological baggage. It’s not about their personal lives. This is going to be about their professions and how they strategize. It’s about playing the game, playing the legal game. We don’t really go home with them a lot.”

Tierney has some help on the legal side of things from her family. “My father’s a lawyer, my brother’s a lawyer. I’ve been hearing stories about judges and what my father did in court and who said what to who my entire life. My brother just recently passed the bar. Hopefully I’ll do a good enough job [for them].”

The Whole Truth premieres September 22 on ABC.