Twin Peaks” incorporated a lot of strange characters, past and present. But one of the oddest may be… Donald Trump.

No, you didn’t blink and miss him in Showtime’s recent revival of the ‘90s series. He pops up very briefly, unnamed, in co-creator Mark Frost’s new novel, “Twin Peaks: The Final Dossier,” which fills in a good deal of the show’s missing mythology. In Frost’s earlier book, 2016’s “The Secret History of Twin Peaks,” it turned out that, centuries ago, explorers Lewis & Clark had apparently been in possession of the jade ring that went on to portend bad things for everyone from Laura Palmer to Dougie. In “The Final Dossier,” we don’t learn exactly what happened as a result of our current president coming upon this totem of doom, but that’s hardly the only thing left open-ended after the narrative has come to an end.

Frost got on the phone with Variety to discuss resuming his writing and producing partnership with director David Lynch, offer solid clues as to how we should read the elliptical ending to Showtime’s part of the saga and explain why he brought so many characters back the new book that didn’t make it onto the show itself. (If you’ve been waiting 25 years to find out whatever happened to Donna, or for an answer to the question “Annie, are you okay?,” you’ll get it in “The Final Dossier.”)

There aren’t a lot of antecedents for TV series that involve huge amounts of mythology to have follow-up books that both wrap up loose character plotlines and explain some of the mysteries, at least from one of the creators. Can you think of any others like yours? The creators of “Lost” never wrote “Lost: A Final Wrap-up from the Island,” and we never got “The Prisoner: What the Hell Just Happened?”

[Laughs] None comes to mind. No, honestly, this may be sort of a one-off.

There was recently an interview with the producer of the series who said that she and David had not read the book yet. Did some of the things that are in the book come from back story that you and David came up with for the series that you just didn’t ultimately work into the script, or was you arriving at all this additional material a matter of: “Mark, we trust you, come up with whatever you want — it’s okay by us”?

I think it’s a little bit of both. David and I talked for a year before we ever started working, so there’s no doubt that some of those ideas [in the new book] came up during that period of time. But also, you know, it was [me saying], “David, you go make the show, and do what you do best, and I’m gonna do that with the books.” So you have to trust your partner.

When the idea of reviving the series still seemed like a pipe dream, did you think of writing books like these, as novelistic sequels or prequels in their own right?

Yeah, I had thought of writing whatever turned into “The Final Dossier” as early as 1991, I think, when we were conceiving and producing the first three books that we did. [There were actually four official spin-off books or audiobooks produced in 1990-91, none directly written by Frost or Lynch.] I had this in the back of my mind. At that point I hadn’t really started a publishing career yet; that happened after “Twin Peaks.” I felt that after 12 books, I was ready to write “The Secret History.” It dovetailed perfectly with what we were doing with the show, and I thought would make a great companion piece, as a way of expanding the Twin Peaks universe for folks, extending it back in time, and also in terms of interior spaces. And I was always thinking, well, then I’m gonna need to write a second book. because there was so much I wasn’t able to address in the first one, because I didn’t want to give anything away about what was coming in “The Return.”

The two books both are in FBI dossier form and both have Agent Tamara Preston (played on the series by Chrysta Bell) sending information she’s compiled to her superior, Gordon Cole (David Lynch’s character). Other than that, they couldn’t be more different. “The Secret History” feels like your magnum opus, spanning more than a century’s worth of conspiracy theories and arcane knowledge about Lewis & Clark, L. Ron Hubbard, Nixon, and UFO lore. “The Final Dossier” dispenses with the historical tangents to just get into the series’ characters — it’s a much more direct act of fan service.

Yeah. Well, I think the easiest analogy is to say “Secret History” was a nine-course tasting menu, and “The Final Dossier” is dessert.

In “The Secret History,” you play some of the historical stuff for arch humor, as it ties into what we know about “Twin Peaks.” And there’s at least one moment of that in “The Final Dossier,” when we find out that no less a historical figure than Donald Trump may have worn the jade ring at some point.

Well, I have to say, I couldn’t resist. as we came toward present-day, I wanted to, if only glancingly, address it.

Do you feel like Trump wearing the ring explains anything about what’s going on in the world right now?

Well, it’s as rational an explanation as I’ve come across.

Some fans were frustrated at how many of the characters from the original series didn’t even come up for mention in the new series. You go into detail about most of those characters in the book. It starts off with Leo’s autopsy, and you go into the story of Windom Earle and Annie that consumed the final season of the original show. Did you and Lynch think it would be too distracting to mention those characters in the series but that the book would be the place to satisfy fan curiosity?

Yes. There are a variety of reasons, which I won’t go into, why people didn’t show up in the new series. My feeling was, well, let’s at least give those characters some love and attention here and satisfy people’s curiosity about them — again, trying to expand the edges of the universe and give it a little more sense of completion. So yeah, that was the motivation for a number of those explorations in the new book.

And you satisfy fan curiosity about Audrey (Sherilyn Fenn), who did show up in the series, but in such a bizarre way, and so disconnected from anything else, that people wondered if she was still in a coma after 25 years and her scenes were all part of a dream sequence from her convalescent bed. Without spoiling too much, it can be said that you reveal that some things are actually as they literally appear with Audrey.

Yeah. I thought it wouldn’t hurt to [go into Audrey’s present-day existence]. That would certainly have come up in Agent Preston’s investigations, so I thought it was a legitimate piece to include.

The series revealed that there haven’t been very many happy endings for the show’s original characters, including Audrey. You made exceptions for a couple everyone was rooting for, Big Ed and Norma, and a couple no one was rooting for, Nadine and Dr. Jacoby, who finally found some peace. Everyone else is unsettled. And that goes for just about all the characters that only come up in your book, like Donna and Annie. Even Doc Hayward (Warren Frost), a character that must have a special place in your heart since he’s played by your father, turns out to have had a difficult personal life between the series. Is it your tendency to resist happily-ever-afters?

Well, I think that that just reflects your feeling about how life goes for people. I concentrated [in “The Final Dossier”] mostly on people from Twin Peaks, not necessarily the newer characters. You want to round out an entire picture of the town. And I mean, how many people do get a happy ending? It’s not a huge percentage across a broad population. Yeah, that’s life.

As far as Dale Cooper’s arc, in the book you go into Cooper’s ongoing quest to be a savior to the women in his life. The narrator, Agent Preston, relates that to Annie, and also to his mother. Of course the narrator can’t go into the events of the final episode, because she is not traveling through time and space with Cooper and Laura Palmer. But did you bring up to Cooper’s desire to save women in “The Final Dossier” to allude to that final quest to save Laura, and whether that is a positive thing, or if it’s a thing that ultimately dooms him?

Well, I would say I didn’t do it accidentally. [Chuckles.] And I think Dale’s psychological history is certainly pertinent to everything he’s done during the course of the series. Some of that was touched on a bit in the book that we did about Agent Cooper [in 1991], “My Life, My Tapes.” The point there is that he’s not just a one-dimensional Dudley Do-Right. He’s a complex person who was formed by his experiences, and those shape the choices he made. And some of them may have untold consequences.

There’s an obvious reluctance on your or Lynch’s part to explain the ending of the series. But can you address the tone of how it ends? Most people certainly experienced it as an unhappy ending, if only for the lack of resolution. When Cooper asks what year it is, it seems like maybe he has become unmoored in time the way Philip Jeffries did, which is probably not a happy place to be. And it’s not at all clear Laura has been saved. But then some people have read her final scream as being some sort of positive resolution, if it represents some kind of realization or culmination taking place. Can you say whether you felt it was a tragic ending?

I think you know me well enough to know I don’t like to interpret for people. I prefer to let the ending just stand for itself. The one thing I would say is that actions have consequences. And some of them are unintended. And Cooper’s push to finish what he saw as his quest harkens back to me to some of the essence of Greek tragedy. It may have been an act of hubris, albeit a well-intentioned one, to think that you can somehow play with time.

Although the book can’t go there, to the events of that final episode, it’s surprising that you do deal in the book with the aftermath of Cooper going back in time to pluck Laura Palmer away from being murdered. And it turns out that there is no major butterfly effect in the town of Twin Peaks as a result of Laura not having been murdered. That opens up a host of questions. But it will probably be a relief for people who were worried, after the series ended, that basically the last 25 years never happened.

No, that would have been way too easy. I guess I just tried to wrap my mind around how something like this [Laura never having been found] would ripple through the real world. And that was what I came up with.

The question about the show in the early ‘90s was, is it a nighttime soap with some supernatural overtones, or a supernatural story with some soap overtones? “The Return” definitely veered even more toward the mythology than the original series, yet your new book does satisfy that need for people to get some resolution on the kind of soapier character narratives. When you think back, do you think ABC fully understood they were getting what would turn into an all-out supernatural thriller?

My guess is, that’s a better question for them. I wasn’t privy to what their thinking was. I know that, for the most part, their thinking about the show was fairly conventional, and that was what was so vexing to them about it, that it didn’t fit into a box that they knew how to label. And TV broadcast networks were not overly celebrated at the time for innovation and narrative daring. So, I mean, God bless ‘em for taking a chance to begin with, but from that point on, I think they were just kind of hanging on. I remember the looks on some of the faces as they saw things that came through. Showtime completely embraced the idea of “whatever.” They’d read the scripts, so they knew what they were getting into, and they were more than happy to go on the ride. They embraced it fully and were superb at every stage of the experience.

How much time did you spend writing the books? And did being away during production mean you were ever surprised and delighted by what Lynch had come up with on-set?

Oh yeah — every week. I thought the whole thing was a joy to watch, and I loved it as much as the most ardent fan. But I mean, I was there for probably a good 40 percent of production. I had to spend a certain amount of time doing [“Secret History”], but I tried to be there as much as I could. The first book was about a year, maybe a little longer. The second book was probably six months.

You’re probably aware that a lot of people analyze the Lynch/Frost partnership and think that you must be the guy who provides the conventional narrative glue, given your series TV background and books, and David is the guy who does the surreal. Does that irk you, or is there at least a germ of truth in that perception?

I think it’s a little reductive. I think if you were to look at my solo work, you’d see plenty of mythological and larger spiritual influences, and I bring all that to the table from the start of the show onward. In terms of narrative structure, yeah, that is a particular strength of mine, and that does match up well with David’s profoundly different visual orientation. So there’s stuff that’s definitely there to complement each other. But David has great ideas, and he’s also tremendously funny. I’m always wary of trying to break it down into black and white. It’s much more complex than that. You can’t extract the various ingredients of a soup after the soup is made.

When the number of episodes was announced, fans thought, “Wow, 18 seems like a lot.” And as the show was winding down, and it became apparent the series wasn’t going to tie up all the loose ends, everyone was thinking, “Wait, only 18? Twenty-five seems more like it.” Even your new book, at 150 pages, is a little shorter than people might like. But obviously the only time constraints you had were on yourselves. Do you think you ultimately gave people about the right amount?

Yes. You may know we wrote one big script, and that’s how it was presented to Showtime. We didn’t break it down into the number of hours. But my recollection is that David always had the number 18 in his mind. So I don’t know if that influenced his final thinking, but that’s where we ended up. As Carl [Harry Dean Stanton’s character] would say: “What is, is.”

You put “final” in the title of “The Final Dossier.” Is this final-final, as far as you’re concerned? Do you feel like the series and the book provide a place where the story should end, or would you like to revisit it?

I don’t know. I mean, I didn’t know 25 years ago, or however many it is now, whether I’d ever want to revisit it then. So, I think what I’ve learned is, leave the door open, and see where you end up. And that’s what I plan to do now.

You’re not already thinking about how to revisit “Twin Peaks” 25 years from now?

Well, if I look at my calendar that far ahead, it’s probably not a good idea to make plans. You never know.