'Chicago P.D.' season 4 episode 8 spoilers: Squad deals with highly-skilled killer; Will Lindsay and Halstead get engaged soon?

A highly-trained killer wages war against the Chicago Police Department in the upcoming episode of NBC's hit procedural drama "Chicago P.D." season 4.
Titled "A Shot Heard Round The World," next week's episode will see the team deal with a huge threat. According to the official synopsis for episode 8, a young officer is shot dead in the lobby of an apartment building. As the investigation progresses, Intelligence looks into the latest known offenders who have made threats to the police. However, when a second officer is murdered, the team eventually realizes that they are dealing with a killer who is highly trained and knowledgeable.
Voight (Jason Beghe) tries to keep the case under wraps as they deal with Chicago's ever-present war against the authorities, while Lindsay (Sophia Bush) confronts Antonio (Jon Seda) after learning about his new job with the State's Attorney.
Lindsay and Halstead (Jesse Lee Soffer) recently decided to take their relationship to another level by moving in together. Many Linstead fans were delighted by the couple's new milestone and assumed that they will soon get engaged, but Soffer clarified that it might not happen anytime soon.
"People live together for a while," he told TV Line. "We're getting a little ahead of ourselves. They're career cops. Hold on a second! Let them focus on their professionalism for a minute! [Laughs]"
Speaking with the same publication, Bush also hinted that Lindsay's family will be coming back to the picture and their arrival will lead to more revelations. "There was a whole storyline last year where Bunny told Erin that her father wanted to meet her, and it just didn't make it in. The cases were too big and complicated. So they're saying that they might bring it back in now. All that I know so far is that [Bunny] tells me he's in Chicago and wants to meet me. I know that a couple of facts that Erin thought she knew about her dad turn out to not be true."
Tune in to all-new episodes of "Chicago P.D." season 4 every Wednesday night at 10 p.m. ET on NBC.