SPOILER ALERT: Do not read if you have not yet watched “Zarak Mosadek,” the 18th episode of the fifth season of “The Blacklist.”

A bag of bones, a time jump and a brutal character death — ever since the midseason finale of NBC’s “The Blacklist,” viewers have been waiting to see how the story of Ian Garvey (Jonny Coyne), a.k.a. the man who killed Tom Keen (Ryan Eggold), would unfold. While Wednesday night’s episode, “Zarak Mosadek,” didn’t solve the mystery of the duffel bag, it did bring the audience one step closer to answers while introducing an even bigger question in the form of Raymond Reddington’s (James Spader) long lost daughter.

The character of Jennifer Reddington was first mentioned three years ago, but has never physically surfaced — despite Red dedicating his resources to find her — until now. She showed up in the final scene of “Zarak Mosadek” as Lilly (Fiona Dourif), the woman Liz (Megan Boone) witnessed Garvey going out of his way to visit at a hot wings place. Liz brought Lilly to her apartment to question her about what she knew, but was in for a shock herself when she realized the person she was interrogating was her half-sister.

“This is a storyline that has been long gestating,” Bokenkamp says. “It’s something we often talk about in the writers room: who that Jennifer character is, when would be a good time to bring her back. As the story plays out you’ll see it’s a very organic, personal story and the reason for the ‘why now’ is a really compelling one.”

Heading into next week’s episode, “Ian Garvey: Conclusion,” “The Blacklist” creator Jon Bokenkamp talks with Variety about Liz’s ongoing quest for revenge, how the Lilly reveal will affect Red and Liz, how he crafted a big bad like Ian Garvey and what’s still to come in the final few episodes of the season.

The audience has known for a long time that Red has another daughter, but how long have you planned for her to be tied to Ian Garvey?

Really all season. When we created Ian Garvey we knew he wouldn’t just be some bad guy, he would have to be somebody who mattered in some way. Exactly who he is and how he fits into the picture remains to be seen, but we wanted it to ultimately become an emotional story. It’s going to be really compelling. This new character that we meet as Lilly is a key that is going to unlock a pretty cool door into the mythology of the show.

Is there a potential for her to return to the show past these two episodes?

Yes, absolutely. That’s one of the big reasons to tune in, is to find out who this woman is, what she knows, and how she can either help Elizabeth Keen or hurt Raymond Reddington and we’ll just have to see how that plays out. But it is an interesting new dynamic and a new character that has potentially a lot of answers in the history of her relationship — or lack of relationship — with this man who is her father. It opens some really interesting storytelling for us.

Is Ian Garvey a character you’ve had in your head for a long time?

Certainly all season and really at the end of last season we had talked about him. So yes, he has been part of the landscape of the show for some time.

How do you go about conceptualizing a “big bad” of that magnitude compared to other Blacklisters?

What we always think is interesting, whether it’s Alexander Kirk [Ulrich Thomsen] or Mr. Kaplan [Susan Blommaert] or even Berlin [Peter Stormare] from season 2, these people aren’t usually just bad guys who want money and guns and power. They ultimately turn out to be fairly small stories — intimate stories about people — about family and about their history. So, in terms of building Garvey, that is a character that we knew he was a US marshal, we knew he was incredibly corrupt and incredibly well connected, and that he didn’t know the whole story. Like our audience he’s trying desperately to figure out what the hell is going on. In terms of really building him out, Johnny Coyne is somebody we looked at even as early as the pilot. We almost cast him as the character named Ranko Zamani [Jamie Jackson]. He was the first Blacklister and we thought he would be great but for whatever reason it didn’t work out, and as we were casting this we landed on Johnny Coyne. I called him and we had a great conversation and we were lucky enough in this case to write to, and for, and with that actor, which is something you don’t always have the opportunity to do because the casting process is often very late. He’s somebody we’ve liked for a long time; we think he’s got a great presence, he’s super specific and he has been a great addition to the show.

Liz has obviously been on a mission to get this guy; how does learning about her half-sister alter that mission?

It opens up the possibilities — not only [does it raise] questions that are complex for Liz, but meeting this woman, trying to figure out how she’s connected to Garvey, what she knows, what Garvey knows, is something that opens a door into even more possibilities and yet at the same time it’s pushing us towards answers. Liz is in a really great place. Oddly enough, remember it’s Liz who has met this young woman, not Red. Liz has stated very clearly that she is also in search of this duffel bag and has no intent of letting it go, and Reddington feels the same way. They may be working alongside each other but they have different goals. This is now somebody that Liz has come into contact with that nobody else on the show knows about, and that might be an interesting asset for Liz.

What can you preview about Red’s reaction?

He has been searching for Jennifer Reddington with no success. All we know after tonight’s episode is that Liz has stumbled across this person who claims to be her sister. What Liz does with that information and what information this character has remains to be seen. A few weeks ago we saw Liz bring in her therapist to kind of call upon for help in the future. She’s sort of been arching towards a rather Reddington-like headspace. We have to anticipate that Liz might not be totally above-board in all the things she does in the coming episodes, just like Red.

Could this reveal create a bigger wedge between Liz and Red?

I think so. The blush that came off at the beginning of the season was this acceptance that this man is her father. It doesn’t change who she is — she’s a grown woman — and yet she’s trying to accept him. What we’ve seen over and over throughout the course of the season is that Reddington is only able to share so much. He is a criminal and she is an FBI agent. He said early on that there’s always going to be things he’s not telling her. And I think that is what is becoming increasingly difficult for Liz. That is also insanely compacted by the fact that her husband was murdered in search of this truth. That was the early turning point. That’s where a lot of this darkness came from. The moment Tom died everything changed for Liz. It’s increasingly difficult for her to understand why Reddington is trying to keep the contents of this duffel bag so private.

Heading into next week, the title “Ian Garvey: Conclusion” has the word conclusion in it, so is it safe to assume Garvey’s story ends? And what about the bones in the duffel bag?

What’s interesting is we still have another four episodes after this and so the story is certainly not over. What is coming next week in the next episode, what really I’m most excited about is a — I don’t know if I would call it a standoff — but a trap that Reddington has in mind. Sort of a magic trick that he’s hoping to pull off to confront Garvey. We are going to end the stalemate, and the gloves between these two men are going to come off. The outcome of this next episode is going to pivot the back part of the season in a really muscular and fresh way.

Often people who are on a journey of revenge don’t know what to do with themselves after they’ve actually gotten their revenge. Have you had conversations about what Liz look like after she’s exacted hers?

We had a whole episode where Liz went out to the woods to sort of lose herself and move past it and sit with that anger — that hatred that she has. That has been one of the things that’s been most interesting to watch Megan play, is that arc. She is someone desperately trying to hold onto any sense of normalcy and trying to be an above-the-board cop. But at the same time her husband has been murdered, her daughter has been sent away to live with somebody else, and she’s working with the most wanted man in the world. It’s becoming incredibly difficult for her to stay above the waterline. Her thirst for revenge, which Red has warned her about, is unhealthy and will get her no real answers or conclusion. It’s a dangerous slope that she’s on, and Reddington is completely aware of that.

Were you surprised at how passionately fans reacted to Tom’s death? Did it alter the way you told the Ian Garvey story at all?

No, I loved how people felt about it. It was hard. It was really hard to do; it was hard for the show. I remember back when Alan Alda died on our show, and he’s a TV legend. Alan Alda is a great actor. We were lucky to have him and we blew him up. But that’s what the story called for. Sometimes it’s very difficult. Ryan was with us from the pilot, is an incredibly intricate part of the recipe that has made the success of the show, and yet it felt inevitable that this needed to happen. It felt like his character — I don’t want to say that we sacrificed him as some sort of story engine because that’s not the case, but it did fuel Liz in a way that we’ve really embraced and had a lot of fun with and has allowed for her to grow — for better or worse — in a new direction.

How far do you have to plot ahead on a serialized-procedural mix like this?

When we start the season we know our end of the season, we know our midpoint, and we know a couple of other signposts that we want to hit along the way. I don’t know how else we could do it if we didn’t know at the bare minimum those two points, a fall cliffhanger, and a bulls-eye of what we’re aiming for at the end of the season. Along the way we sometimes wander and along the way we sometimes improvise a little bit. Finding ourselves painted into corners is oftentimes not only terrifying but exhilarating, and some of our best stories come from that. But it is something we think about a lot and it is meticulously plotted. It is difficult sometimes to find the right balance of procedural versus serialized, because it is a procedural. Every week we have a new bad guy and it’s rare that we do a two-parter or that we wander from that formula. It’s always a bit of a high-wire act in terms of how much of the serialized story, with the mythology and the characters we want to tell, versus who is the next great creep of the week that we can’t resist portraying.

Have you created signposts for future seasons at this point or do you take it year by year?

In the same way we look at a season, we’ve thought about the whole series and we’ve had conversations with everyone involved. We definitely have an end game in mind, but we’re certainly in no race to get there. It would be impossible to write the show if we were just making it up. I know that probably sounds like a sales line but it is the truth. You can look back at the show, specifically with Wednesday’s episode, and we’ve introduced a character that we introduced three years ago. Oftentimes these things take time. We don’t always know exactly when that character’s going to reemerge or where that storyline will come back, but there is a bible in our writers room that tracks every character, every plotline. If we didn’t have our endgame in mind it would be very difficult to tell the story we’re telling.

“The Blacklist” airs Wednesdays at 8 p.m. on NBC.