Chicago P.D.'s two-hour fall finale ended with a very unwelcome blast from the past for Erin Lindsay (Sophia Bush). At the end of the double episode, Lindsay responds to a text message from her mother Bunny (Markie Post) only to have the news sprung on her that her father is back in town and wants to meet up.

Bunny blurts the information out without much buildup, after an earlier meeting with Lindsay and Halstead (Jesse Lee Soffer) — which was Bunny's first formal introduction to her daughter's boyfriend — was abruptly cut short when Lindsay and Halstead had to respond to the shooting of a police officer. But, how long has she been sitting on this news? And why does Lindsay's father want to get in touch with her? (Remember those mysterious flowers Lindsay received in last week's episode? Yeah.)

We don't get answers to any of those questions, as the episode ends with a reaction shot of Lindsay, mouth agape. But chatted with Bush to discuss Lindsay's reaction to the news, as well as her take on Antonio's departure and how her relationship with Voight (Jason Beghe) has changed this season. Check out our Q&A below.

Chicago P.D.: How did Antonio say goodbye?

After Bunny drops this bombshell on Lindsay, is she ready to welcome her dad back into her life?
Sophia Bush: It's something that Bunny really springs on her. It's not something Erin's been seeking out. She certainly has not been in the position of looking for her dad. She's survived for 30 years without him and does have a great, almost adoptive relationship with Voight. But, her mother, in typical Bunny fashion, shows up and just, like, throws a hand grenade into the room and says that she's back in contact with him and that he wants to meet Erin.

What's going through Lindsay's mind in that moment?
It's such an interesting position to be placed in, because Bunny has begun that conversation unbeknownst to [Lindsay], and [she] has to deal with the fallout one way or another. And it does create a moment of anxiety, because what do you do in that situation? What's the natural response? Does she want to know this man? What if he lets her down in real life in the way that he did in her imagination, and would it be worse? Because, if you imagine something about someone, at least they can be no worse than you've imagined. And you never know who a person's going to be in reality. And also, why now? Does he want something? Is he prone to taking advantage of the people in his life the way that Bunny is? Can Erin handle two people like that? It's a lot for her to put on her plate. And so, by the time Bunny has said, "Your dad's in town, he wants to meet you," it's a little bit of a gut punch. And then in the next episode, we see where that goes.

Last week, we saw Lindsay get a bouquet of flowers as well as a phone call from someone unknown. She makes a connection between the area code and her father, but did she ever suspect those might be from him?

Bush: The note that I got about that was not to assume that it was him. ... It was that kind of throwaway moment of like, "God, that's strange. The only thing I know about my dad actually has to do with Leavenworth." ... But as far as Erin knows, he doesn't know what she does. He doesn't know she lives in Chicago. This is all just Bunny's mess that Erin of course will have to mop up.

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Halstead is obviously very protective of Lindsay. How do you think he will react to her father trying to re-enter her life?
Bush: Jay obviously has Erin's best interests at heart and is a very solid person, and also can be a little hotheaded. I think there is definitely that protective instinct for him. The character that he is goes to suspicion very quickly in situations like this. So the dynamic that we have is Voight obviously having a back story with her mother and father, and Jay not trusting anything that comes from Bunny, and also wanting to protect Erin emotionally because it's very much like, boy, she's had a hell of a year. She lost Justin. Everyone's really so wounded in the family space, so I think he definitely wants to make sure that this doesn't go badly for her.

Speaking of Lindsay and Voight, at the beginning of the season, Lindsay basically put her career on the line to, we assume, help Voight cover up a murder. Did that put them on more of an even playing field?
Yes, certainly. ... I think that she went so far outside of her comfort zone of knowing what is right and wrong, and protection. And while she doesn't love him any less, she's also I think a little more realistic about how safe or not safe he is for her, and just clear that, after what she had to do, there are no favors owed anymore.

We lose probably 10 minutes an episode of material that we film, and ... [there are] two scenes that I'm so sad about. In the finale of last year, the scene between Lindsay and Burgess, when Burgess finds Lindsay in tears over Justin, was much longer. And I just loved the scene for Marina [Squerciati] and I. I thought it was so awesome, and so sad that there was great material from that that we lost. And then, the scene in the premiere, when Voight comes to see Lindsay at her apartment at the end, was also much longer. There were many stops and starts. It was a very hard conversation for Hank and Erin to have as this pseudo father-daughter duo, as coworkers, as now a murderer and an accessory to murder. There was so much in it. And we don't get any more than 42 minutes, so it was a little more addressed there, and in some of the dialogue that disappeared as it got truncated, I did say to him, "We're even now." I had this whole speech about being grateful to him for saving my life and always wanting to be able to repay the favor. But like, now we're even. And it was a very clear admission of, I love you, but I just did something for you that makes me struggle to love myself, to be OK with myself. We were so bummed when it was deleted.

Do you know if the show is going to revisit that storyline at all, or whether Lindsay and Voight's secret will come back to haunt them?
No, they really haven't talked about it. And truly, I do think that it was a great cliffhanger and it's a great storyline. But I think the reality of it, once it got out of the creative space like, "This is a great hook," it was like, "Oh man, we're doing something really dark." I read the script and I was like, I don't know how to do this. I have to do this, because it's my job, but how do I wrap my head around this event? So I think we were happy to kind of move on from that very extreme moment.

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Wednesday's episode also features Burgess (Marina Squerciati) finally joining Intelligence. Will we see her and Lindsay working closely together?
Bush: The Burgess and Lindsay storyline is — first of all, totally selfishly, for me and Marina, it's just so much fun. I'm so invested in her experience because I love the character of Burgess and I'm so happy. And Lindsay loves that this girl who's worked her ass off and deserves it is gonna come up. ... Lindsay's incredibly proud of her. She's stoked. We're friends. They've really bonded, and it's nice to have her as an ally and it's nice to be her ally as well.

What impact will Antonio's departure have on the team as Jon Seda heads over to Chicago Justice?
We hate it. I feel terrible, because this is the worst interview question. I don't even know how to talk about how it affects the team, because I'm just so bummed. We're all just so bummed. We love Jon so much. I definitely said to him, like, "Man, whatever your secret sauce is, you are the golden goose of the Dick Wolf universe. You started on Fire. You went off to P.D." Voight was brought in as an adversary for Antonio! I'm like, "You created the cop stuff on Fire and then you brought Chicago P.D. to us, and then you're going to do Justice. If you become a doctor, then you will have jumped the shark." We were crying laughing. Jon is just so lovely and talented and watchable and even-keeled and smart and thoughtful. I am in no way surprised that Dick Wolf would want him to go and launch the next part of his franchise.

It also makes sense, in certain character senses. At the beginning of our show, there was a huge emphasis on Antonio's family, but, because we're a cop show, the actors who played his family were never going to be series regulars on our cast. And, as they deserved to, they're going to go after jobs where they can be series regulars. So, members of Antonio's family got jobs in other cities and then could no longer come work on our show. So, to service [that in the show], the reason they disappeared, Antonio got a divorce, and now he's divorced and his family can't exactly come back. It got very confusing, because in his personal life he got walled in a little bit, just by the sort of practicalities of our script. And I'm excited for Jon for what world cracks open for Antonio on a new show, where they can begin to take more liberties and he can have a life outside of our unit.

Chicago P.D. returns Wednesday, Jan. 3 at 10/9c on NBC.