After everything, it doesn’t look like it’ll be anything supernatural that does DC’s Legends of Tomorrow’s John Constantine in, but just regular old lung cancer.

As viewers learned last week, the chain-smoking exorcist has been stricken by an aggressive, advanced onslaught of the disease thanks to the otherworldly machinations of Astra, the woman who blames Constantine for his failure to rescue her from hell. The reveal culminated with a harrowing scene that found the Matt Ryan character violently coughing up blood on the floor of his old house, and it’s his struggles with and determination to kick the disease that promises to drive much of Constantine’s storyline for the rest of this season.

“At this point, Astra sees John as a complete waste of space and absolutely the person who ruined her life, which is always a fun way to start a relationship for sure,” shares Olivia Swann, who joined the series as Astra in last season’s finale. “She sees him as this guy who has this air about him that he wants to save everyone, but for her it’s not about that. He was the one who put her in the situation, so therefore, he doesn’t get to save her. She sees him as this anomaly in her life, which made it such a hardship, and she needs to eradicate that.”

It’s not the sort of thing that we’re accustomed to seeing the often self-serving Constantine fight against…at least not on TV. But fans of the Hellblazer comic will immediately recognize the lung cancer as a reference to “Dangerous Habits,” the iconic storyline which started with the antihero being diagnosed with terminal lung cancer.

“For Matt Ryan’s character, Constantine, we wanted to give him one of the iconic storylines from the comics where he gets lung cancer and he’s going to try to do everything he can in the most John Constantine-type way to get out of it,” explains writer Grainne Godfree, who cowrote tonight’s episode, “Mortal Khanbat.” “We put Ray and Gary on that storyline with him because we thought that John’s dark, brooding energy coupled well with Ray and Gary being goofballs. John wants to just be miserable and drink alone, and they’re not going to let him do that.”

Fans of NBC’s Constantine may know that the prematurely cancelled series, which also starred Ryan, intended to adapt “Dangerous Habits” in a later season. (Ryan has said that it’s a favorite storyline of his.) While it seems safe to say that Legends’ take on the story will probably be considerably different from the very dark, very mature Garth Ennis storyline, it’s something the show’s writing team seems excited to take on.

“It’s very important to Matt Ryan,” shares executive producer Phil Klemmer. “He is the world’s leading expert on all things Constantine. In fact, he probably would hand you a book if you were having trouble remembering something—he has it in his bag at all times. For us, it’s a balance because we want to honor (the Hellblazer storyline), but at the same time, we want to break new ground as well. Hopefully, we found the right balance with that. There’s no predicting where we’re headed based on the books, but it was a great launching point.”

That launching point, tonight’s new episode, also happens to be the directorial debut of actress Caity Lotz. While Constantine’s storyline is a big part of the hour, the rest of the episode is heavy on gunplay and vehicles, in what the director says is a tribute to ’90s-era Hong Kong action movies.

“I had like a John Woo-style episode,” shares Lotz. “There’s massive action in the episode. The episode was humongous and there are two very different storylines happening that are both pretty intense.”

“When it’s your moment to shine, you bring this intensity and focus,” Klemmer explains. “The nice thing that we’re able to do as writers is that we know Caity. We know her strengths. We know her appetites and aesthetics, so we can tailor make (an episode for her). Caity’s obviously pretty good at action, so we can give her a John Woo, ’90s Hong Kong, Hard Boiled kind of episode. That glove fit her perfectly.”

With an episode that splits its runtime between slick action and a more character-driven storyline that finds one of its more hardened characters suddenly vulnerable, it could have been difficult to strike the right balance. To address this, Lotz kept both storylines separate in her mind and on the set.

“The action (in the first storyline) was huge,” Lotz reveals. “We had to cut some cool motorcycle stuff, which I hope they release. There’s a lot of practical effects—a lot of squibs and air guns blowing stuff up. You’re tracking out each story so specifically, and I would break down the scripts and almost make my own separate script for just John’s storyline. I would literally cut it out and treat it like its own little movie. I’d kind of keep them separate.”

While the Arrowverse is known for letting its stars step behind the director’s chair—Dana Panabaker, David Ramsey and David Harewood have all directed episodes of their shows this season—it’s clear that Lotz’s time in the role made an impression.

“It was so fun to be on set,” says Godfree. “Caity smashed it. She did an amazing job. She was so prepared, and so creative with the camera. It was lovely to see.”

“That was the first time I met Caity, when she directed my scenes in the episode,” admits Swann. “I was terrified. But she was just so chill and so calm. I was like, ‘Okay, great, this woman knows exactly what she’s doing.’ It was a breeze. There was a sense that because she’s an actor, she could work so well with me and Matt. She knew exactly what to say to help us get to where she wanted. It was just so easy.”

It’s clear that what won’t be easy is Constantine’s mental and physical battle with cancer, though it seems unlikely we’ll be seeing him undergoing chemotherapy, radiation treatment or any of the other challenges a typical cancer patient endures. Nor is he the type of person to go gentle into that good night. That’s good since Ryan’s take on Constantine has been beloved by DC fans since he was first cast in the role in 2014. And they’re far from the only ones who love him.

“I love Matt so much as an actor and person that I feel like that has to color how Sara feels about John Constantine,” Lotz reveals. “I think she’s happy to have him on the ship, especially with the stuff that they’ve been dealing with. I think Sara understands him because she’s always been a lone wolf, so she gets what he’s like. It’s been good to have him around.”

Let’s just hope that John doesn’t have to go through too much hell to stay.

"Mortal Khanbat" airs tonight on DC's Legends of Tomorrow at 9 p.m. (8 p.m.) on The CW. Be sure to visit our official DC's Legends of Tomorrow page for more news, features and articles on the Waverider's journeys.