SHIELD is on fire. There's smoke and dust in the air, the top secret base is burning, and Daisy Johnson is fighting one of SHIELD's own: former director Jeffrey Mace. Pursuing him down a hallway, she takes a punch, jumping up and off a pillar for a stronger advantage...

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“ Can you trust anything? Can you trust us at all?

Chloe Bennet as Daisy Johnson, Ming-Na Wen as Melinda May, Clark Gregg as Phil Coulson, Henry Simmons as Alphonso “Mack” MacKenzie, Iain De Caestecker as Leo Fitz and Elizabeth Henstridge as Jemma Simmons on Marvel's Agents of SHIELD

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Marvel Cinematic Universe: Every Upcoming Movie and TV Show 22 IMAGES

And, cut.Chloe Bennet readies for another take, doing a couple dry runs of Quake's superhero attack pose to get even more amped up for the next run-through of the stunt scene. The camera resets and Quake advances on her adversary once more, this time even more intense than the version they shot previously."That's the one," says co-showrunner Jed Whedon, who makes his directorial debut for the culmination of Season 4's "L.M.D." pod, Tuesday's "Self Control." Up next, the fight advances to the SHIELD lab.My visit to Marvel's Agents of SHIELD's set was toward the end of production on this cornerstone episode, and what I was witnessing was just one small snippet of an ambitious fight scene that took two days to film -- a first for the ABC/Marvel series. With the cliffhanger at the end of last week's "The Man Behind the Shield" revealing that anyone within SHIELD could be an L.M.D. version of themselves, "Self Control" will feature plenty of situations where agent fights against agent, friend fights against friend."When you start the L.M.D. pod, you're like, what are all the things we could do? You don't want to do the ones that have been done, and you don't want to leave any on the table. We had an idea early of what are the bombs you can drop with this and how do we subvert those expectations," Whedon told me. "It's the zombie movie moment of, 'Which of us is a zombie? We all are.' That was a moment we knew we wanted to have early on. We knew we wanted that to be our jumping off point."The L.M.D. arc has been toying with the audience's perception of reality since the beginning, first by replacing Melinda May (Ming-Na Wen) with a robotic version and culminating in now Fitz (Iain De Caestecker) and Simmons (Elizabeth Henstridge) being the only two characters left standing against the L.M.D.s controlled by Radcliffe (John Hannah) and Aida (Mallory Jansen).But Whedon cautions that not even last week's cliffhanger ending can necessarily be trusted. After all, who's to say it's not Simmons and Fitz who are the L.M.D.s, and this is actually part of Radcliffe's elaborate ruse to turn agent against agent? "Can you trust anything? Can you trust us at all? No, you can never trust us," Whedon said with a chuckle in response to that theory."What goes down in the second pod, I would have to say so far has been so exciting, so mind-blowing," said Clark Gregg, who plays Phil Coulson. "This sounds like spiel, but the construct that they've come up with, the pieces that were set up, did not prepare us for the way it was going to turn our entire world upside down and basically make the wildest fantasies you could have about using all the pieces that were set up in these first three seasons come true, and basically everything's in play. For the people who have been here since the beginning, you're going to see some stuff that only you can appreciate."Season 4 of Agents of SHIELD has focused on the nature of identity and reality, first with Ghost Rider Robbie Reyes, and now with Radcliffe, Aida and the Life Model Decoy program. It's dredged up dark parts of the core characters' backstories, from Mack's tragic loss of his daughter Hope to Fitz's troubled relationship with his father, and Whedon promises there will be payoff to all the reflection on the past: "There's a reason we're bringing those out into the foreground."The February 21st episode will set up the third and final pod of episodes this season, transitioning to a new storyline. Though Whedon stayed mum on what that theme would be, wanting to maintain the surprise for audiences, he does promise it "all ties together thematically.""This next pod is very relevant," said Bennet. "It's definitely a theme that I think has been kind of hopping around in pop culture at the moment. But it's kind of like a fun Marvel take on that. For all those people who wished to see these characters in a different light, this is going to be the time for that to happen."More than just being relevant, the final pod of Season 4 is designed to specifically reward loyal fans of the series. There will be a lot of changes and everything will get "mixed up," but it also will pay off storylines that have been left hanging for seasons.Beyond just the "Philinda" ship being realized through an L.M.D. twist, Gregg teased that Hydra will come back in a way that "will surprise the crap out of people." Whedon also hinted that the Gravitonium cliffhanger from Season 1 might finally be revisited: "We would not be doing our jobs as well as we could if we left that unanswered.""We move so fast and we move past stuff, but when you get that thing that you care about called back to, there's a reward there that you deserve. For us, it's fun to play in that world," said Whedon. "These were conversations that we were obsessed with and that we bent our minds into pretzels over two years ago."Previewed Bennet: "The last seven episodes are by far going to be some of my favorite of the whole series because it's really going to reward fans who have been with us from the beginning, and it's really fun."

Terri Schwartz is Entertainment Editor at IGN. Talk to her on Twitter at @Terri_Schwartz