TV

Sophia Bush trades high fashion for dress blues in ‘Chicago PD’

Sophia Bush spent nine seasons playing fashion designer Brooke Davis on “One Tree Hill” — so it’s fair to say her role as Det. Erin Lindsay on the new NBC drama “Chicago PD” is a complete 180.

Sophia Bush with co-stars Jesse Lee Soffer, Patrick Fleuger, Jason Beghe and Kurt Naebig (back to the camera).

“My weekly process has gone from having to squeeze in three fittings to having one fitting every three weeks just to try on different shirts and sweaters because I’m always in jeans and trail boots,” Bush says over tea at The Plaza Hotel. “My thrice-weekly activities become going to the shooting range with the SWAT team.”

But Bush — an avid shooter — fit right into the action-packed “Chicago PD” (10 p.m. Wednesdays on Ch. 4), which centers on an elite intelligence unit run by Sgt. Hank Voight (Jason Beghe). It premiered last week to a respectable 8.6 million viewers and is spun off from “Chicago Fire,” the latest product of the Dick Wolf brain trust (which also includes the “Law & Order” franchise).

“It’s different than his other shows. It’s really gritty, it’s muddy, everything’s gray,” Bush says of its Wolf pedigree. “I feel like on so many of those other procedurals things are very black and white and very neat. It feels more like a cable show or at least an action movie.”

That gray has a lot to do with Voight, who after being sent to jail on corruption charges in an arc on “Chicago Fire,” is now inexplicably out of prison and reinstated on the force, where his crime-solving tactics are not exactly by-the-books.

Bush’s Lindsay also has a murky history with Voight — she credits him with “saving her life,” turning her from bad girl to criminal informant to cop — details of her past which are only slowly revealed.

“It won’t happen quickly,” Bush says. “In episode six, she gives [her partner Det. Jay Halstead] the most back story that she’s given to anyone and it still just scratches the surface. It talks about her life from when she met Voight, but still doesn’t give him anything about who she was before that.”

Because the District 21 precinct office of “Chicago PD” is only a fictional two-and-a half blocks from Firehouse 51 of “Chicago Fire,” the two shows are primed for crossovers. The characters share the same after-hours watering hole (Molly’s) and fan boards are already campaigning for an inter-series romance between Lindsay and Kelly Severide (Taylor Kinney). Even Wolf’s New York-based franchise, “Law & Order: SVU” will have a “Chicago PD” crossover, with Kelli Giddish and Ice-T coming to the Windy City to advise on a special victims case.

Bush, who was a fan of “Chicago Fire” before filming, says all the back-and-forth between the two series feels very natural.

“It feels like we’ve always been doing it,” she says. “I was addicted [to the first season], which also kind of makes for an interesting experience when you’re doing a crossover because you know the show so well that it doesn’t feel foreign to step inside of it.”

To prepare for the role, Bush also spent a lot of time with female cops in Chicago to learn what the police academy experience was like for them, what they faced from men as females on the force as well as the details of working undercover cases.

“You can’t believe how little we know as citizens about how risky their jobs are every day. Now every time I see a police officer I want to hug them,” she says, noting the show strives for authenticity. “We do everything for the small percentage of police that will be watching our show.

“We want them to be proud . . . to buy everything that we’re doing.”