[Warning: This story contains spoilers from Tuesday's Agents of SHIELD, "Scars," and Avengers: Age of Ultron.]

War is coming between the Inhumans and SHIELD.

During Tuesday's penultimate episode of ABC's Agents of SHIELD, Coulson (Clark Gregg) revealed the truth behind the mysterious Theta Protocol to be a helecarrier that was hidden away only to be used in a case of emergency — as seen in feature counterpart Avengers: Age of Ultron.

With Lincoln (Luke Mitchell) recovered from his time held captive at the Hydra base, Coulson arranges a sit-down between SHIELD and the Inhuman leader Jiaying (Dichen Lachman). Gonzales (Edward James Olmos) meets with Jiaying on the behalf of SHIELD, but in an unexpected turn of events, finds himself impaled with pieces of a Diviner when Jiaying destroys a Terrigen crystal in front of him. To cover up the murder, Jiaying shoots herself in the shoulder twice and proclaims war against SHIELD when her Inhuman compatriots arrive.

The Hollywood Reportercaught up with executive producer Jeffrey Bell to discuss Theta Protocol, the mysterious Kree Stone and Jiaying's act of war.

The Theta Protocol finally is revealed as a helicarrier Coulson kept hidden away that Fury uses to save the citizens of Sokovia in Age of Ultron. Why was Coulson so secretive about keeping a helicarrier hidden away from everyone?

We played this as most people don't know Fury (Samuel L. Jackson) is alive; this was a Fury-driven thing. SHIELD has always operated in secrecy, and that's the way that went down. It was supposed to be for an in-case-of-emergency-break-glass situation. And that happened, and it seemed like a big cool idea. The idea of hiding an elephant seemed like a fun idea, and that's what we tried to do.

The Kree stone is meant to wipe out Inhumans. Was this a fail-safe in case there wasn't a renewal?

Nothing is ever as it seems. Ever. Or we're not doing our job. And it is something that is a cool interesting thing we're going to explore. It wasn't so much a fail-safe in case there wasn't a season three (because we always thought that there was) so much as we're getting into the end of the season and we're bringing in this new mysterious item — what is that? Is it what she says it is, or is it something else? It has an unusual ability to go from solid to liquid and back. There's something more going on there.

When Coulson tries to talk to May (Ming-Na Wen) about why he kept Theta Protocol a secret, she kind of blows him off and says, "Skye's (Chloe Bennet) living proof that you lost control of yourself after the alien blood." What's going on with May's feelings toward Coulson as this point?

She's upset that Coulson was in contact with her ex-husband and kept that a secret. Because SHIELD is full of secrets, and she has her own, she was reporting back to Fury all of last season — watching him — so she doesn't have a lot of moral high-ground to say, "How dare you keep secrets from me.” So when he's apologizing about keeping secrets about Theta Protocol, she's like, “Well, no, I can forgive that,” it's more that Coulson had been in contact with her ex-husband that bothers her. Which is an obvious emotional issue for Agent May. That's why she feels betrayed. She understands why he does it, but she's still hurt by it.

Looking at Fitz (Iain De Caestecker), at the end of last season he suffered from a traumatic injury, and at the beginning of season two he still wasn't quite himself. Where is he in terms of recovery? Is he back to his former self? Or has he adapted to his new, post-injury life?

There were two components with what happened to Fitz. We consulted top neurosurgeons and neurologists to help design the kind of drama that affected Fitz and part one was the lack of oxygen to the brain which can affect speech and certain motor skills. On top of that, he talked about PTSD and how that's a separate issue. The brain can heal and recover, but we've also seen that when Fitz gets in stressful situations, he's suddenly back to a more stammering version of himself. The PTSD part of it still felt relevant. All of this has made Fitz bolder; he's taking risks. He finally went out on a mission on his own. But he still struggles in certain situations. Particularly around Ward, he has trouble speaking — and for us, that was part of his growth. It wasn't so much about getting him back to where he was or returning him to who he was in season one because back then, FitzSimmons was one person. This season was about splitting them up and letting each of them develop into a whole person on their own. You see Simmons (Elizabeth Henstridge) wanting to take out Ward and do things on her own. We wanted to grow them into their own people, but that's never a linear process. Sometimes it's two steps forward and one step back.

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Mack (Henry Simmons) quit SHIELD since Coulson was still in charge. He believes Coulson isn't in control of himself because he was brought to life using alien blood. Is there something to Mack's accusations?

He had a really bad thing happen to him involving alien stuff, and as he looks around the landscape, anyone who has had any involvement with an alien has not turned out well. For him to have that opinion, he's achieved it honestly, and when he says to Coulson, "I love you, I respect you, I just can't work for you," I think that's all very genuine.

At the end of the episode, Jiaying makes a daring move and turns against Gonzales' nature. Was this out of fear of the Inhumans being indexed? Or a thought of losing Skye to SHIELD? Or both?

It's really the bigger picture. What Jiaying says is true. She has set up a community in the middle of nowhere so they would be left alone. We know that her experience in the past with SHIELD — even though we know it was Hydra masked as SHIELD — was horrible. So now here she is with SHIELD showing up at her doorstep saying, "Hi, we don't want to hurt you, but we do want to index you, and we do want to monitor you," and that didn't work well for her. She is trying to protect her people. I don't think she's a bad person for doing it, but the way she's doing it seems a little bit suspect.

Raina's (Ruth Negga) visions up to this point have been accurate, and it looks like she saw this coming with Jiaying. She seems willing to turn over a new leaf but is hindered by her past and who she was. What can we expect for Raina in the finale?

You hit it on the head. This is a woman who has been manipulative at every step along the way and now she's having these visions and seems to be telling the truth, but she's also been her own worst enemy. The question is, can we trust Raina or will she be up to her old tricks?

Kara (Maya Stojan) and Ward (Brett Dalton) kidnapped Bobbi (Adrianne Palicki). Is this a vendetta against Bobbi?

All will be revealed.

Is there anything you can tease for the finale next?

It's big. It's emotional. There are some twists and turns, some surprises. I'm excited to see how people react to it.

What are your SHIELD season finale theories? Sound off in the comments below. Agents of SHIELD airs Tuesdays at 9 p.m. on ABC.