The CW series The Flash is back for Season 4, and while Barry Allen (Grant Gustin) has spent six months in the Speed Force, Iris (Candice Patton), Wally (Keiynan Lonsdale), aka Kid Flash, Joe (Jesse L. Martin) and Cisco (Carlos Valdes), aka Vibe, have taken over protecting Central City. But when Cisco decides to break Barry out of the Speed Force to help them fight off a powerful villain, they quickly realizes that Barry is not the same Barry as before, and that that will take some adjustment for everyone.

During this 1-on-1 phone interview with Collider, executive producer Todd Helbing shared some insights into Season 4, what it means for a hero to be reborn, what kind of leader Iris has become in Barry’s absence, WestAllen couples therapy, the upcoming four-hour cross-over episode, tension with Wally, getting to learn more about Harry Wells (Tom Cavanagh), the Cisco-Gypsy-Breacher dynamic and what Danny Trejo brings to that, and what makes The Thinker a different kind of villain.

Collider: We’ve seen a hero being born, when Barry Allen first became The Flash, but what does it mean for him to be reborn this season?

TODD HELBING: Well, the last season got pretty dark. We started to see that, as it was happening, and we had a lot of discussions about how to get back to the real fun of having Barry Allen love being The Flash and to get that baggage that he’s been carrying around off of his shoulders. When he made that sacrifice, at the end of Season 3, whatever experience he had in the Speed Force, allowed him to deal with all of that. So, when he comes out of it, he really is like a new guy. He’s a new Barry Allen. He’s much more akin to the Season 1 Barry Allen, and he loves being The Flash and loves his powers and loves being a part of the team. It’s been a lot of fun and really a lot of joy to write this version of Barry Allen.

In Barry’s absence, what kind of leader has Iris been, and how will Barry feel about her leading the team, when he returns?

HELBING: Iris stepped up and became team leader. It’s so fun to see her in STAR Labs, driving the ship, calling the shots and being the team leader. Vibe stepped up. Kid Flash stepped up. They’re the Central City resident superheroes, and they’re working with Joe. Seeing that team work as they do, for six months, they’ve become a well-oiled machine in Barry’s absence. So, when Barry comes out, you can imagine if, all of a sudden, the leader reappears and is more than willing, ready and happy about taking down the bad guys as The Flash, that he’s not really used to this new dynamic, at all, and he has to figure out what his role is going to be on the team now, moving forward. It’s a lot of fun to see how all of that works itself out.

Especially knowing that they are headed down the path to a wedding, how do Barry and Iris get back on the same page? What does WestAllen couples therapy actually look like?

HELBING: They have a lot of work to do. It’s not like you can just disappear for six months, after sending out save-the-date cards, and then come back and be like, “Let’s go pick out our wedding gifts!” It’s gonna take some time and some conversations and some emotional work, and it felt like putting them in couples therapy would be the perfect place for them to work out their issues while also simultaneously letting us have a lot of fun with those two and their new dynamic. You’ll see exactly what they have to work through to get back on track.

We know that the four-way crossover between Arrow, The Flash, Supergirl and Legends of Tomorrow will include the long-awaited WestAllen wedding. What can you say to tease Team Flash’s role and the wedding in that crossover, and whether there are any particularly fun moments involving The Flash cast that most stand out for you?

HELBING: I don’t know if there is any one moment. We’re telling a four-hour movie. In the past, an Arrow episode felt like an Arrow episode, a Flash episode felt like a Flash episode, and Legends felt like Legends. With this cross-over, we’re telling it like a collective story. It’s so fun to see them all together, working together and being together for four hours. While we’re progressing the narrative on all four shows, it’s really this amazing throughline for everybody. I don’t think I have a favorite moment. I haven’t watched all of the dailies. We’re still shooting it. The stuff I’ve seen is amazing. Every year, we have to outdo ourselves and it’s a huge challenge, but I think that we did, this year.

How does Wally feel about being the only speedster around Central City, at least for a little bit, and then how does he feel about no longer being the only speedster around again?

HELBING: Barry doesn’t have to just do work with Iris. He has to do work with everybody, and Wally is no exception. When you are the speedster in town and you’re still Kid Flash, but you want to be The Flash, and then The Flash returns, it’s an interesting dynamic. This guy taught him. He was his mentor, in a lot of ways. So, to have your mentor return and want to lead the ship again, Wally is gonna bristle a little bit.

We know that we’re going to get to delve a little bit deeper into Harry this season. What was it about the Harrison Wells of Earth-2 that made you want to stick with him, in particular, and what will his journey be, in Season 4?

HELBING: One of my favorite relationships is the Harry-Cisco relationship. It’s so fueled with annoyance, on both sides, so that was certainly attractive. We felt like there was still more story to tell with Harry, and that we could take him on a great emotional journey, this year, where maybe Harry needs to work on his interpersonal skills, a little bit. We’re going to round him out, as a person, and that’s been a lot of fun. When he shows up, there’s a reason why he’s come back to Earth-1 and why he is folded into the team that really speaks to his journey, throughout the season.

I’m good with as many versions of Harrison Wells are necessary to keep Tom Cavanagh on the show.

HELBING: Well, we certainly do not disappoint this season, in that regard. All I can say is that Tom outdoes himself, every time. Some of the stuff that he’s done this year, so far, is unbelievably hilarious.

What can you say to tease the Cisco-Gypsy-Breacher dynamic, and what does Danny Trejo bring to that, just simply by being Danny Trejo?

HELBING: I’ve gotta be honest, it was crazy being on set with him. I’ve been such a fan, for so long. There’s one classic shot with him, that I can’t get into, but that you’ll know when you see it because it’s classic Danny Trejo. His comic chops are so great. He’s Gypsy’s father, and Cisco and Gypsy’s relationship has blossomed. They’ve been dating for eight months now, but I don’t think he enjoys anybody dating his daughter, much less Cisco. That creates a little bit of tension between the two. Their storyline in Episode 4 may be one of my favorite things that we’ve ever done on the show.

What makes The Thinker a different kind of villain than we’ve seen on The Flash, and what does he want?

HELBING: I can’t really get into what he wants yet, but this guy is the smartest man in the world. He’s not a speedster. He can’t compete with Barry, physically. It’s the fastest man alive vs. the fastest mind alive, so he can out-think anybody. He knows where people are gonna be, he knows how they’re gonna react, and he knows what scenarios he can put them in to create other scenarios that he needs. It’s not like he can see the future, but he has thought through every outcome. He is not only the man who built the chess board, but he built the chess pieces, and then he puts them on the board where he wants them, so he can play the moves when he needs to. It’s a lot of fun, psychologically, in how that washes over the team.

The Flash airs on Tuesday nights on The CW.