The much-loved hit series Sherlock is returning for Season 4 in 2017, and actor Benedict Cumberbatch and co-creators Steven Moffat and Mark Gatiss were recently at Comic-Con to give hints about what fans can expect from the three upcoming episodes. Never ones to reveal secrets, the three were cagey in their responses, but their passion for the material and characters was definitely clear.

During the roundtable interviews, they talked about the evolution of Sherlock Holmes, why Moriarty still weighs on him, that Season 4 is so dark that it’s “end of the universe darkness,” how Toby Jones’ villain is different from previous ones on the series, what Sherlock might think, if he ever encountered Doctor Strange, and why they would love to continue on with the series, but never at the cost of quality.

Question: Steven and Mark, when you’re dealing with the evolution of the character, over the seasons, what are the things that Sherlock Holmes can never change?

STEVEN MOFFAT: His coat and his underwear. What is immutable about Sherlock Holmes? He favors reason over emotion, but actually underneath that, there is a lot of emotion going on. You can’t suddenly make him ordinary because he would hate that. He’s not suddenly going to be somebody else. I don’t know that he precisely softens. He becomes more human and more adept at fitting in with a lot of people, but he remains separate from the human race because he finds that a better place to observe that from. He stays on the mountain top because there, he can see clearly.

MARK GATISS: That’s what makes characters interesting. If Sherlock had started out being a straightforward man, we wouldn’t be talking about him now. If he became one, that would be interesting. But you have to give him somewhere to go, as Doyle did. The rather rarified, strange young man that Dr. Watson meets, right at the beginning, is not the same man who counts John Watson as his only friend. He can do things much better now, but he can never become one of us. Otherwise, he’s not Sherlock Holmes.

MOFFAT: He can be wise and funny. He wasn’t, at the beginning. But later on, he’s got a bantering relationship with loads of people. He’s got a wisdom that he didn’t have in the early stage. But he stays on the mountain top, and he will die up there. He’s not going to change that.

Benedict, what’s it been like to have a character you get to do a dance with, every few years, and have it feel familiar, but also new and different, each time?

BENEDICT CUMBERBATCH: It’s lovely. It’s familiar, and yet we wouldn’t do it, if it was just the same steps. That’s what brilliant about the writing. The keep challenging us and it keeps evolving. You can go quite far with a character that started off as morally, sociopathically, and obsessively work-based. You can perfect genius because genius is not perfection. On his level and his practice and his methodology, it’s almost inhuman. So, that’s been a fantastic arc to play, and boy does it go somewhere in this series. To be able to come back to that and to reunite the band, and have it be familiar but different, is great.

How different is Sherlock now, from the Sherlock that we first met?

CUMBERBATCH: He has moved from being someone who was sociopathic, work-obsessed and slightly amoral, into being someone who has a certain degree of a private life, which is very, very private, with The Woman, or Irene Adler. With his interactions with people, he’s better at what he does. He has to understand the world. That’s very much John’s influence on him. But like a lot of the friendships and relationships in that world, it’s born out of necessity. It makes him better. There’s a pragmatism to it. It’s not whimsical or sentimental. It’s born out of necessity.

Why is Moriarty someone who’s still weighing on Sherlock, even though he’s no longer there?

CUMBERBATCH: I think it’s the first time he really meets his match, and it’s scarred him. It’s a nemesis, and nemeses play large in your psychology. They’re not just physical entities who are actually present. It’s about the fear of them. And I think that’s why Moriarty really succeeds. He’s terrorized Sherlock’s mind. It’s fear that lives on.

Does he have a strange respect for Moriarty?

CUMBERBATCH: Absolutely! Yeah, absolutely! They’re different sides of the same coin, and he recognizes that. Sherlock is on the side of the angels, but don’t think he’s one of them. He uses similar means, but it seems to be for a better purpose, one would hope.

Are you touching on any specific Sherlock Holmes stories, in Season 4?

MOFFAT: All three stories are based, as usual, to a greater or lesser extent, on Doyle’s originals, but you have to work out which bits.

Benedict, what’s it like to work with writers like Steven Moffat and Mark Gatiss, who are so passionate about what they’re doing with Sherlock?

CUMBERBATCH: It’s great because there is a very strong reference point for any detail and keeping yourself in check with the canon. I go back to the books for specific references and for evolutions, which are there in the literature. It just comes across in every aspect of the writing, from how dark it gets to how funny it is to how rich the characterizations and relationships are. Their joy of it is the audience’s joy, and therefore, our joy in playing it. It gives you a good day at the office.

Season 4 has been described as the darkest season yet.

CUMBERBATCH: Without a doubt.

How dark does it get?

CUMBERBATCH: Myopically dark. You’re talking about the end of the universe darkness. You can’t see in front of you and would walk into everything dark.

MOFFAT: We turned the lights off to save money, so you can’t really see it. It’s the same show. Hopefully, there are lots of laughs and lots of great personal stuff, but it is explicitly a darker season. You’ll have to wait and see.

How different would you say Toby Jones’ villain is from the villains and adversaries we’ve seen previously?

MOFFAT: He’s completely different. It’s a completely different character. He’s the darkest villain we’ve had. There was always something charming and engaging about Moriarty. There was something fascinating and actually amoral, rather than immoral, about Charles Augustus Magnussen. This guy is the purest evil. Sherlock is actually appalled by him. He’s the most evil villain we’ve had. I don’t think that when you see it, you will disagree. He’s horrific.

GATISS: It’s an interesting thing to chart. We made our Moriarty very different to Doyle’s. He’s Irish, and he brings all his charm, his twinkle and his humor to it while he’s also terrifying. Magnussen was a very blank, chilling business man. He doesn’t see what he’s doing as evil. Toby is doing something very interesting. She’s an avuncular, funny seeming man with terrible teeth. We’ve given him terrible teeth, which are symbolic of the rot inside him. It’s a great complex, shaded character. You’re not quite sure what the relationship is with him.

Mark, what drives Mycroft to continue to spy on Sherlock?

GATISS: It’s love and affection, and it’s a big family bond. They’re a strange family. Rather than what you expect, we explicitly wanted the parents to be lovely people who have discovered that they have these two very odd children who are a bit like Niles and Frasier Crane. They’ve come from a very warm family environment. So, even though he doesn’t express it very well, and he uses the machinery of the state to monitor him, it comes from a place of love. What he wants to do is gather him into the embrace of the establishment. Because Sherlock is a loose canon, it drives him nuts.

If Sherlock met Doctor Strange, what would he say about him?

CUMBERBATCH: That’s a really good question. Rather like the Ancient One, I think Sherlock would see quite a few of the missing links in Strange’s life. I think he’d be able to expose his motivations and flaws very quickly, as he can with anybody he meets. Whether he’d be that interested in Doctor Strange, as we meet him at the beginning of his origin story, I don’t know. As far as defending the world, as we know it, from other dimensional threats, I don’t think Sherlock would really know about that. That’s where that interaction would stop.

You’ve all gotten busier and busier, since you started on Sherlock. Can this keep going?

CUMBERBATCH: We’ll see. We’ll see how this series lands. It’s been great fun to come back and do it. How it will continue in the future, who knows? It’s not just about what any of us want. It’s about what’s actually right for the show, to be honest, and that has to be judged very carefully. Think about the very limited but classic British output of certain shows, and there aren’t that many of them. It’s a painful thing to say, but maybe Series 4 is it. Who knows? I don’t know. I don’t want to say this is it because we have too much fun doing it. But generally, we have to see how this lands. And the actors aren’t the only ones who are busy. Mark and Steven are pretty tied up. Mark is an actor, as well as a producer and writer. It’s all of us being stretched in different directions. Also, this has run longer than most American series. You don’t want to compromise it by continually doing it, just because we could carry it on. There’s lots of stuff to weigh. It’s not just about what we want to do. It’s about what’s right. We’ll see. Really, we will have to see. No one has decided on it, so there’s no yes or no to an end or a beginning.

MOFFAT: We have to take it one season at a time. We don’t know what the future will be, and it’s not entirely down to us. Hopefully, we’ll do more. I find it hard to imagine that we won’t. But in terms of a specific plan, there are ideas that we haven’t gotten to yet.

GATISS: We’ve been percolating a few things. We’ve got some ideas.

So, it doesn’t feel like you’re done then?

MOFFAT: I don’t know that it ever does. If you get to the point on a show that you feel like you’re done, you’ve probably gone past the point that you should have stopped. You should stop full speed, as it were, and leap off the train while it’s still going, rather than letting it grind to a halt. We won’t do that. We would never do a series of this without it passing our inspection first. We have to be so excited about it, before we start talking to the others. But there are ideas, so who knows? We’ll see.