SPOILER ALERT: This interview contains major spoilers from “How Do I Live,” the Season 21 finale of ABC’s “Grey’s Anatomy.”

“Grey’s Anatomy” is no stranger to shocking season finales. But for the Season 21 finale of the venerable ABC medical drama, showrunner Meg Marinis wanted to pay homage to some of “Grey’s” greatest hits — a perpetrator holding doctors hostage in an OR during a life-saving procedure; couples falling in and out of love in the middle of a medical emergency; a superior sleeping with an intern before realizing they were an intern; and, of course, a potentially catastrophic explosion on the surgical floor of Grey Sloan Memorial Hospital.

“In the past, we’ve had people threaten the hospital — we’ve seen Gary Clark in the shooter episode (at the end of Season 6),” Marinis tells Variety. “But we were like, ‘What does it look like when a destroyed mom does it?’ So we did a twist on this story and wanted to do a nostalgic ‘Grey’s’ finale where you don’t know who lives and who dies.”

Thursday’s finale revolved around Dr. Amelia Shepherd’s (Caterina Scorsone) latest “impossible case”: Dylan Gatlin (Sophia Kopera), a 9-year-old patient who, following complications from surgery to treat a cavernous angioma, was diagnosed with locked-in syndrome. After becoming fed up with Amelia and Dr. Beltran’s (Natalie Morales) repeated insistence on waiting to see whether Dylan’s intracranial bleeding would resolve on its own, Dylan’s mother, Jenna (Piper Perabo), decided to take matters into her own hands, stealing a tank full of acetylene from her husband’s truck and threatening to blow up the hospital if Amelia did not save her daughter.

With an assist from her nephew, Dr. Lucas Adams (Niko Terho) — who could only watch helplessly as Jenna held an explosive to his ex-girlfriend Dr. Simone Griffith’s (Alexi Floyd) chest — Amelia is able to stop Dylan’s bleeding. (Ellen Pompeo’s Dr. Meredith Grey, who is no stranger to hostage situations or potential explosions in the OR, even jumps in to deliver some fresh frozen plasma to help save Dylan.) In a state of equal parts relief and disbelief, Jenna fell to her knees and let go of the tank, and she was promptly arrested.

The police verified Jenna’s assertion that the tank had been empty all along, but for some reason, no one had thought to check whether the valve had been opened. In the final two episodes of Season 13, Meredith witnessed an explosion that caused a fire on an upper floor of the hospital from the parking lot. The final moments of Season 21 parallel that moment, with Meredith again looking up in horror from the parking lot after another explosion wipes out part of the surgical floor.

Below, Marinis breaks down all of the developments in that jam-packed finale, including what Meredith’s new deal with Catherine (Debbie Allen) will mean for Pompeo’s future involvement with the series. Having joined “Grey’s” in 2006 as a writer’s PA who has risen through the ranks to become the current showrunner, Marinis also opens up about her working relationship with Pompeo, as well as how she is approaching potentially bringing back more beloved characters for the show’s record-extending 22nd season, premiering this fall.

Piper Perabo delivers a heartbreaking portrayal of a mother whose desperation leads her to hold hostage the doctors who are responsible for her child’s care. The character could have easily been characterized as a pure villain, but viewers will inevitably feel these fleeting moments of sympathy for this woman who has clearly spiraled out of control. How did you think about crafting Jenna’s multi-episode arc, and what stands out to you about Piper’s performance?

It gave me the chills every time they arrested her, which is a tribute to Piper’s performance. Obviously, when we were in discussions of casting her, we filled her in on the entire story and let her know that it would be the deterioration of a character that you see in her eyes. When we see her in that first episode, she is put together and she’s got makeup on. Her kid is having surgery, so she’s worried. And then in the second episode — and Piper was very involved in this — she had them take curls out of her hair, and she had dark circles and less makeup.

But we couldn’t go too far with her performance until the very last episode where in Act I, when she turns and you see that look on her face, you’re like, “Oh, that’s the moment she makes the decision that she’s going to take this hospital down.” Piper was a great collaborative partner, and I am so grateful that she joined our show for three episodes because she’s so talented. She is someone who looks like the girl next door, but then in a second could just turn. She gave that performance that you see in the cut, even when the camera was on the other people. She did it 35 times in a row.

In a first for “Grey’s,” this season, Teddy (Kim Raver) and Owen (Kevin McKidd) decided to experiment with an open marriage in order to save their marriage. Teddy tried exploring her attraction to Dr. Cass Beckman (Sophia Bush) but ultimately called off their fling. Owen, however, hooked up with his childhood friend, Nora (Floriana Lima), who later becomes Teddy’s patient. Where did the inspiration for the storyline come from? Did you always know that you were going to end with Teddy wanting to split from Owen?

No, we actually thought it was going to end differently. And with the performances that Kim and Kevin were giving, they blew me away all season long with those difficult marriage conversations that they had. Our design at the beginning of the season was that this marriage hasn’t been historically happy, so let’s actually see it play out in real time and see what often happens, which is people use band-aid solutions to fix something that is broken in itself. I think that open marriage has worked for some people, but on television we often see that it’s a mistake.

It also was a fun way to get other interesting guest cast to highlight and illuminate what Teddy wasn’t getting from Owen and what Owen wasn’t getting from Teddy. A lot of it is that Teddy now has the job that he used to have. That power dynamic has been difficult for them. They’re two full-time, high-stress working parents with two small children. They don’t prioritize their marriage, and this is the consequence of that. And when other people were prioritizing them, they saw, “Oh, there is something wrong here. It’s not necessarily that we want to be with these people, but we’re looking at each other not the way we should be looking at each other.”

Teddy has spent years and years choosing Owen — sometimes at the expense of her own job and her own happiness. What epiphany did she have in these last few episodes that has allowed her to reach the conclusion that she has to choose herself over Owen for once? Did seeing Owen and Nora together in the hospital bed give Teddy any kind of clarity?

I think when she sees the two of them together at the end of the (penultimate) episode, and then she had the surgery to perform, it’s this moment of, “Can I do this?” I think the second that she realized that she could do the surgery and that she could do anything, she realized, “OK, I could walk away. I came up with this amazing surgery. I saved the woman that slept with my husband. I am strong enough.” I think before this moment, there was fear that she wasn’t strong enough to do it. And in this episode, she realizes that she can do it. It’s very hard and painful, but that speech is so strong. I hope women watch it everywhere and make the right decision for themselves. She’s such a strong character, and I think that sometimes she puts herself second for him.

Owen was clearly blindsided by this conversation, but to be fair, he had it coming. Where do you see them going from here?

I don’t think they know yet. Obviously, the dynamic may shift, knowing what happens in the hospital at the end of the finale. Obviously, (what takes priority is) who’s injured, who’s taking care of whom, and how Teddy navigates that as chief. I think it’s going to be difficult, but I do think that as writers we’re interested in seeing what it looks like when the two are apart for a moment. It doesn’t mean that they won’t eventually find their way back to each other, because this is “Grey’s.” We could go on for another decade!

In the penultimate episode, shortly after Lucas had just dumped her, Simone hooked up with a handsome stranger (Trevor Jackson) at Joe’s Bar — and, naturally, that man is now one of the new surgical interns at Grey Sloan. What new complications will that new intern create for Simone and Lucas going forward?

Well, Lucas has to find out first, right? And the last time we saw Lucas, he was running down a hallway trying to prevent an explosion. So we have to find out what happens there, but I think this is really, really messy for Simone. This is Meredith Grey messy. I think that it’s even messier, because from the little that we’ve seen of this new character, he does have an arrogance that will rival other doctors in the hospital. He may not be the easiest, most agreeable, most obedient intern, so that will throw another wrench into the game.

Have you named this new intern already, or are we going to find out his name next season?

You’ll find out his name next season.

Following the end of “Station 19,” Ben Warren (Jason Winston George) returned to Grey Sloan to work as a probationary surgeon, but Bailey (Chandra Wilson) reveals that Teddy is not recommending him to continue his residency at the hospital due to his tendency to break protocols. What complications did you want to create for Ben in his return to the medical field? And given that cliffhanger, will he really be leaving Grey Sloan?

He was outside the hospital when that explosion went off, so we know he’s alive. But he doesn’t have a job, so he’s going through an emotional explosion. What we wanted to see for him coming back was that it wasn’t going to be as easy as he assumed, and also the difficulty of having to work side-by-side with your wife who is in a position of authority over you. I think they were able to navigate that fairly well. There were a few bumps in the road, but we wanted to tell a story where Ben did not want to ask for special treatment from Bailey.

And because he did it his way, the renegade way, it caused him to end up in a load of trouble. But the person who made that decision was Teddy, and Teddy has had an emotional year. So I think there’s something to be said, now that she’s finally able to choose herself and put that part of her life aside: Did she make the right decision? And how helpful will Ben be in this chaotic moment when the hospital is essentially on fire?

Winston (Anthony Hill) and Jules (Adelaide Kane) was a new, potentially romantic pairing that seemed to come straight out of left field this season. What did you want to accomplish by pairing the two of them together?

Since Meredith and (Patrick Dempsey’s) Derek and the early years of the show, we have not really had that power dynamic in a romantic relationship. (Camilla Luddington’s) Jo and (Justin Chambers’) Alex had that a little bit, and that’s clearly frowned upon in today’s world. Winston is a younger attending, so it’s not like there’s a huge age difference, but there is a difference in that he’s an attending and she’s an intern. So we were really interested in exploring that in today’s world and calling out that it’s wrong.

Winston knows that it’s wrong and he tries to do the right thing, but what he thinks is doing the right thing is actually at the expense of her education. We were like, “Well, she has to call him out on that.” If you look closely, there’s debate on whether we think this is one-sided. Jules pauses very deliberately before she says, “The lines were very clear for me.” If you watch that episode where she takes him to the rooftop, I feel like she was crossing the line there for him. So there have been some moments where I’m not sure it was just one-sided, but Winston was really trying to stay behind the line because he is a standup guy.

Jo and Link (Chris Carmack) also got married in the penultimate episode, and we learn after their little hospital honeymoon that they are expecting twin girls — but, of course, Link is operating on a patient right before the explosion happens.

With Jo and Link, they had known each other for 20 years, but their relationship fast-forwarded really quickly. It went from, “Oh my gosh, we do want to be together” to a month or two later, “We’re pregnant?!” And all of a sudden, it was twins and they were struggling with the way they looked at having kids differently, and then she had a complication. And finally, they got on the same page and decided to get married. So I feel like it’s the calm before the storm again for them. We’re “Grey’s,” we’re mean! It’s a cliffhanger, but we find out they’re having girls, which is such a nice moment. They had a beautiful wedding, and she was a beautiful pregnant bride.

Meredith decides against selling her shares in the hospital and instead makes a new deal with Catherine that will allow her to spend more time in Seattle and back at Grey Sloan — all while continuing her Alzheimer’s research. Does Meredith’s new deal with Catherine mean that we will be seeing a little more of her next season, or is Ellen still set to appear in seven episodes?

We’ll see her as much as we can get her. She’s always welcome to come with us. She’s family. We loved watching her get a star on Hollywood Blvd. — very, very deserved. I wanted to see Meredith not only continuing her research on Alzheimer’s, which is super important and relevant right now, but I also miss seeing her in the OR — and not necessarily doing the most groundbreaking surgery of all time. I missed just seeing her in the OR and teaching, and especially with this class of residents that she chose, it was also a way to get her back into Seattle in order to see that side of her. Obviously, we’ll get to see Scott Speedman, because Meredith and Nick are still together.

You’ve intentionally chosen to write multi-episode arcs for Meredith, rather than giving her a bunch of one-off appearances. How do you navigate those conversations with Ellen about her future on-screen involvement with the show?

The multi-episode arcs are also much better for her schedule, so she knows when she’s going to be there and when she’s not. We speak at the beginning of the season, and I share with her what the show is doing as a whole. If I’ve shared it with Shonda (Rhimes) and Debbie (Allen), our producing director, I’ll share what I can with Ellen — she’s an executive producer — and we’ll have a great conversation about it. We check in with each other throughout the season on the phone, via text. She does the voiceover. She’ll call me and be like, “Is this the right tense in the voiceover?” And I’m like, “It’s the right tense.” We have a very close relationship and we speak often, so when I know that a block of episodes is coming down the road for her, I’ll call her while I’m writing them and I’ll walk her through the story.

Ellen spoke with me recently ahead of her Hollywood Walk of Fame ceremony, and she was very candid about how she has found herself pushing back against some of the new writing on “Grey’s” that seems at odds with the Meredith character that she and Shonda had created together. She was specifically referring to a recent storyline involving Lena Waithe’s character, which she vehemently disagreed with. How have you, as a showrunner, navigated those kinds of disagreements with her? And how difficult is it to incorporate Meredith into the show when she comes in and out as much as she does?

I wouldn’t say that it’s difficult to incorporate her coming in and out. Obviously, it’s the decision of whether to show her in Boston or show her in Seattle that is hard to sometimes get organized and figure out. But for years, she has always wanted to be a part of the storytelling — and she has been. A lot of amazing stories that have aired have come from a collaboration between us and Ellen, and that’s why she’s been a part of the show for so long. She cares so much. She’s played this character for 21 years, so she has a history with this character more than I have a history with this character. I’ve watched her for 21 years and I’ve written for her for several years, but I would hope that she would speak up if something didn’t feel organic.

And I was there that day for that particular story. I knew it was difficult, and I knew it was not quite what Meredith would do, but that’s what interested me in it. She and I walked through it and made some line changes, and I feel like you can see on screen the emotion that went into the story, and it was a beautiful performance. For me, it was wrapped up in the fact that she has a much different relationship with Alzheimer’s disease than any of our characters, and now she has Nick in her life and a different relationship with organ recipients and that part of medicine as well, so that’s where (the story) came from. I know it was a long discussion on set, but we got to a beautiful place, and I appreciate when she does that. These people have played these characters for so long. If they didn’t speak up, it would be weird.

Will you be casting a new class of interns between seasons?

We may meet them, but we’re still invested in this now-second year class of residents. As much as I would love to have a cast of 30 series regulars, I don’t think that’s doable for the story and budget. But hopefully, we’ll see some in maybe a recurring role or something like that.

Ever since she left the show in 2014, Sandra Oh has maintained that she does not have any desire to come back to “Grey’s.” But in a recent interview, she admitted that, because people still have so much love for Cristina Yang, she has at least been moved to slightly soften her stance. What did you make of her saying that? And while I’m not saying that you will bring Cristina back per se, how are you approaching any conversations with former cast members about potentially returning to the show one day?

Oh my gosh, I hope she does — and I hope I get to write the episode! She and I have run into each other a couple of times at social events, and she has so much love for the show; she has so much love for the fans. I would hope that one day she’d return, but I think it’s also hard to return to something where you think you’ve closed that door.

What’s so great about a 21-season show is we can surprise the audience (by) bringing back a fan-favorite. There are so many fan-favorite characters that can still come back, even if they die, and the writers’ room is always pitching different people. We try not to do it too much, because then it wouldn’t be as special. They’re all very busy, but I think one of the joys of being able to work on this show is that there is this pool of very talented, beloved characters and actors that, if the timing is right, would come back, especially now that we have this new class of interns. We can play off them as, “Oh my gosh, Addison’s (Kate Walsh) coming to teach us,” or “Jackson’s (Jesse Williams) coming.” It’s also fun to have them interact with the new cast members. We still have great relationships with everybody, and if we can afford it and if they’re available, we’ll bring them back!

This interview has been edited and condensed.