When Greys Anatomy" executive producers Joan Rater and Tony Phelanleft the ABC medical soap to launch their own legal drama, they knew there was at least one aspect of the former series that they wanted to carry over to the new one: the sense of never knowing who is going to come through the door.

Doubt, the new CBS procedural from the wife-and-husband team, is set in a New York boutique law firm that takes on risky social justice cases.

Like in 'Grey's, you never know who will come in needing help, Phelan said. We wanted a show about people who were from various socioeconomic backgrounds. That was really important to us.

The series, which premieres Wednesday, stars Katherine Heigl as Sadie Ellis, a defense attorneywho becomespersonally involved with her latest case and client,played by Steven Pasquale (Rescue Me). The cast is rounded out by Elliott Gould, the chief of the law firm, and Laverne Cox, Dule Hill, Dreama Walker and Kobi Libii, all of whom play lawyers. Cox, it merits noting, is the first-ever transgender actor to play a transgender character in a series regular role on broadcast TV.

Doubt is somewhat inspired by ABCs late 90s-early 00s legal drama, The Practice, which Rater and Phelan devotedly watched early in their relationship.

We really enjoyed watching that show, Rater said, sitting next to her husband at a hotel bar in Pasadena on a recent weekday.We wanted to see more criminal defense lawyers; we wanted to get to know the defendants more...

Doubt attempts to explore the best and worst of the criminal justice system, looking at those who are criminalized and those who are committed to defending them. The imperfections of Americas penal system is an area of focus in which Hollywood has shown growing interest. In addition to HBOs 2016 limited seriesThe Night Of, a number of projects out of Sundance this year also investigate the imperfections of law and order.

The more we can see that people who are in prison are people with families and with dreams and aspirations, I think, is enlightening, Phelan said. Are we, as a country, really about reform and rehabilitation? Or are we about putting people away and throwing away the key and just getting them out of society? And if we are about that, let's just be honest about that. But if we are really about reform and rehabilitation, how do we do that?

The main case to which viewers are introduced involves Billy Brennan (Pasquale), a plastic surgeon who is facing conviction for the first-degree murder of his former girlfriend, who was killed two decades prior. Things grow complicated as the relationship between Billy and Ellisbecomes more intimate.

A similar attorney-client progression in The Night Of came under fire, with critics chiding it as a misguided development.Phelan and Rater say there's something to be said about that kind of intimacy.

The lawyers almost become a lifeline, so inmates develop this, sort of, dependence, Rater said. Sadie knows everything about Billy. They've spent all of this time together and they're both flawed in similar ways. They both have strange upbringings and we and the writers just thought that was interesting. It's a line you are not supposed to cross but the 'what if' of it all How would you negotiate it? How would you deal with the fact that it's so wrong and so taboo and what are the consequences? --is really interesting to us.

Doubt was originally developed for the 2015-16 season, but the pilot was never ordered to series. After undergoing re-development and re-casting (KaDee Strickland and Teddy Sears were replaced with Heigl and Pasquale), its now making it to air with a 13-episode order. It marks a reunion of sorts Phelan and Rater last worked with Heigl when she starred on Greys Anatomy. (Heigl left the series in 2010.)

It was nice just to continue our collaboration because we've known Katherine for 10 years now, Phelan said.

It was just the sort of the magic ingredient that the show needed, Rater said.

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yvonne.villarreal@latimes.com

Twitter: @villarrealy

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Katherine Heigl is only one of the elements of 'Grey's Anatomy' the creators of 'Doubt' brought to CBS legal drama - Los Angeles Times