Twenty-seven years after Back to the Future Part III was released, it's time to go back in time and uncover a hidden adventure that happened between scenes of the final big-screen outing of Marty McFly and Doc Brown.

Back to the Future: Tales from the Time Train is a new comic book series from IDW Publishing, co-written by franchise screenwriter Bob Gale alongside John Barber, with art by Megan Levens. It answers a question fans might have had about the final feature: Just when did Doc, Clara and their kids take the train into the future, as teased in the final scene — and what happened when they got there?

The 1990 film ends with Doc (Christopher Lloyd) and his kids returning in a time-traveling train, only to fly off again. Before they go, Marty (Michael J. Fox) asks if Doc is going back to the future. The scientist responds, "Nope, already been there," the line that would end the film series.

Heat Vision talked to the writers of the series about going back (and forwards) in time to continue the beloved series in comic book form.

IDW has been publishing Back to the Future comics for a couple of years now, but this is the first time you've gotten around to addressing the dangling plot thread of Doc's dialogue at the end of Part III. Was the intention always to get to this point?

Gale: When IDW said to Universal, "We're looking for the license to do Back to the Future," the original pitch to me was, "We will do new adventures with Marty's kids and the next generation of Back to the Future," and I said no, no. We looked into this when we did the Back to the Future video game with Telltale back in 2010, and we determined that fans want to see Marty McFly and Doc Brown and the characters they know and love from the movies. So, I said, "if we're going to do this" — and at the start, it was just going to be a four-issue series — we've had people write in for years with unanswered questions they had from watching the movies. For example, how did Marty and Doc Brown meet? Why did Doc Brown's house burn down? These were things, to me, that were good ideas to do stories about, things that fans wanted to know about.

It was a way for us to stay true to the Back to the Future mythology — I certainly wasn't going to allow the mythology to get screwed up in any way — and the folks at IDW said, "That's a good idea. Let's explore that." By the time the third issue came out, they said, "It's selling pretty well, we're going to expand it to five issues," and then a couple of weeks later, they said, "We're going to make it into an ongoing series." Once they said that, I got with John Barber, who'd been the head writer on the first four, and we started kicking ideas around asking, how do we explore new adventures? That was when IDW said, "We don't want to do little shorts, we're going to have longer arcs." One thing led to another, and we came up with some interesting ideas. John brought a whole lot to the party — sometimes, he would come up with an idea and I'd just make sure the proverbial train stayed on the tracks.

Barber: Except for, they don't have tracks.

Gale: [Laughs] Well, in Back to the Future No. 5, when we showed the first experiment with the Time Train, we definitely had tracks!

Barber: Around the time it was decided to do a bigger story, I pitched this terrible idea. It was a couple of pages, I sent it off, and then the weekend came and I thought, "Wow, that was a terrible idea." [Laughs.] Bob called about a week later, and said, "I want to talk to you about this idea," and I said, "It's not very good, is it?" He was like, "No, it wasn't." We got along pretty well from that point. I'd already figured out at least part of what I'd gotten wrong by that point. I'd written what I thought everyone wanted to see, but it wasn't what anyone wanted to see. We ended up doing 25 issues of the ongoing series, once we'd gotten into the big story, and for the most part, they focused on Marty. Doc was definitely a part of them, but he wasn't the central character. And we were talking about it with our editor, with IDW, and the idea of doing a story about Doc, Clara, Jules and Verne — his whole family — it seemed like a good starting point for a good story. It picks up right at the end of Back to the Future Part III from Doc's point of view —

Gale: — Sort of. We're trying to make sure none of the fans call us out for screwing up the continuity of it. At the end of Back to the Future Part III, when the Time Train flies away, Marty says, "Where you going now, Doc, back to the future?" Doc says, "Nope, already been there." I said to John, "Well, we've gotta pay that off. Doc's already been to the future? We've got to show that."

You had that line in the movie — was there always a story there, or was it simply a joke?

Gale: It's a joke! It's just showmanship. At the end of the first movie, everyone said, "Oh my goodness. Surely you knew you were going to do a sequel by putting that ending in the movie." No! We had no idea anybody would even go! The original script had been rejected 40 times, so we had no idea if anyone was going to show up at the theater when it opened. We just thought, well, this is a very satisfying ending. All your heroes riding off into the proverbial sunset and off to another adventure. But, as [director] Bob Zemeckis frequently points out, if we really knew we were going to do Part II, we would never have had Jennifer get into the car. Because when it comes to figuring out what that movie would be, we said, "What about Jennifer? She's not a particularly well-drawn character in the first movie, and it's not really about her." Eventually, we came to the conclusion, all right, she's going to be unconscious for most of Part II. She's played a much bigger part in the regular comic book series, and we did flesh her out as a full character.

What is it like returning to this material, and finding that you'd seeded the movies with these opportunities for new stories? Is it interesting to come back and re-approach it, or do you curse yourself for leaving these spaces that you feel the need to pay off?

Gale: Both! [Laughs.] Sometimes we tear our hair out and say, "I guess we gotta deal with that." But there are other times where it's great. One of my favorite elements is this one: In the first movie, Marty McFly goes to the Twin Pines Mall, the back of Doc Brown's truck opens up, and the DeLorean comes out. OK. It's a great moment, and everyone remembers it, but think about it: We'd already seen Marty go to Doc's lab. If Doc built the DeLorean in that lab, Marty would already know what it was. But it doesn't, so how does that make sense?

The idea we came up with was, well, Doc has a second lab hidden away. And that led us to a couple more plot elements we could use — it was something that nobody in 30 years since the movie had asked that question. And believe me, I've been to enough Back to the Future events, and been a guest speaker and done interviews, and I thought I'd heard every Back to the Future question. Somehow, we stumbled on this, and Johns and I both said, "Oh, yeah. There's got to be another lab. That's so cool!"

John, you talked about the initial idea and that it was what you thought people wanted to see. When working on properties like this, do you have to silence your inner fan?

Barber: It's a little of that, but one of the fun things about working with Bob is that Bob is so focused on the characters. That's what makes the Back to the Future movies work. It's not just being a fan, but the way I work — I'll happily get into stories about the mechanics of time travel, and what the technical details would be and how it would work, but that can't be the focus. It has to be a consistent world this all takes place in, but the main thing is how does this affect the characters, what are they learning ... It is a time travel movie, but it's a Marty McFly, Doc Brown movie, you know? We can't just do a hollow adventure where they meet Julius Caesar and change history, because it doesn't matter, it doesn't effect them. It's not meaningful.

Gale: The other rule we had is that we don't use time travel to get out of a plot scrape. So if you're up against the wall and terrible stuff is happening, you don't suddenly go back in time and prevent those things from happening. That's kind of cheating. Once you open up yourself to that mechanic, then the audience throws in the towel, going "Aw, they can do anything they want, because they've got a time machine. It's only going to happen because the writers say it's going to happen." It's not coming out of character.

Are you surprised that there's not just a hunger for new Back to the Future, but also the space to tell new stories?

Gale: Yeah! [Laughs.] It's interesting that there is, but the flipside is, what allows you to tell these stories is that the characters are well drawn. Anybody that's a fan of a long-running TV series knows that — you look at a show like Seinfeld. How many years did that show run? It's all about those characters. You just say, "OK, Jerry found a lost dog. We can do a whole episode about that." The characters are so well drawn that, whatever idea you come up with, you put them in certain situations and the plot elements write themselves. You think, "What would Doc Brown do here?" and immediately, it's like, well, here's what Doc would do, sure. [Laughs.]

Back to the Future: Tales from the Time Train No. 1 will be released Dec. 27.