Warning: There will be spoilers ahead for last night’s episode.

A lot has changed since Agents of S.H.I.E.L.D. premiered back in 2013, most notably the size of the show’s core cast. The series went from six core cast members, to one that now consists of nine. Which is why last night’s episode of Agents of S.H.I.E.L.D., “4,722 Hours”, was so impressive. Given the ever-growing cast, it’s rare to see S.H.I.E.L.D. focus on just one character’s story – and yet, they did just that last night. Elizabeth Henstridge (Jemma Simmons) carried last night’s fantastic episode, allowing us to take a break from the team going after Lash & Ward and to focus on the journey Simmons had to endure on an alien planet.

Even more surprising than S.H.I.E.L.D. doing a bottle episode? It was revealed that Simmons wasn’t alone on the alien planet. We knew that there was some sort of being after her – one that we still have plenty of questions about – but what we didn’t know was that there was someone else stuck on the planet with her. Dillon Casey‘s Will, an astronaut that had spent the past fourteen years on the planet. As time went on and the two of them were forced to lean on one another to survive, their relationship naturally developed into something more. While doing interviews for last night’s episode with various outlets, Henstridge talked about what it was filming this episode, what will happen going forward, how desperate Simmons is to rescue Will, and plenty more below.

Given that this episode focused solely on Simmons, Henstridge had the weight of the filming on her shoulders, having to appear in pretty much every scene – with some help from Casey’s Will and the few moments shown with Fitz (Iain De Caestecker). Talking to Entertainment Weekly, Henstridge explained what it was like to film this episode knowing that it was all on her shoulders.

It was definitely very challenging. I always expected it to be challenging. My thought was, “Oh my gosh, Kerry Washington on Scandal, this is what it must be like for her every week! She’s in most of the scenes!” It’s a different mindset. I remember hearing an interview with her that said she was speaking to Ellen Pompeo from Grey’s Anatomy, and she advised Kerry to treat yourself like an athlete. I was like, “I’m one of these women now! I need to treat myself like an athlete.” I just took very good care of myself. We took good care of each other, all the crew and everyone. We were all in the trenches together. We shot it in the desert somewhere in a couple different locations and it was always over 100 degrees. We managed to time it with a heat wave in Los Angeles. It was just crazy shooting conditions. It was cool. It just added to the whole thing. We felt like we had the chance to make something very special, and we were trying to make it as good as possible. We asked a lot of the crew this episode and they just did not disappoint.

One thing that wasn’t entirely explained in last night’s episode was what it was that was after Simmons and Will. Some fans have suggested the planet could have been Ego the Living Planet, something that would make sense, “4,722 Hours” pretty much left the window wide open on that one. Although, according to Henstridge, it appears that we’ll have some answers soon enough.

Will we get more of a sense of what was chasing them and where exactly they were?
Yes. We’ll learn more about that. It will have an impact going forward.

Is there anything you can tease about why the monster appeared to her as an astronaut?
How we’re setting it up is it manipulates you and uses what will sway you. It wanted Simmons to think that NASA had come back so that she would go toward it.

Given that last week’s episode of S.H.I.E.L.D. ended with Simmons telling Fitz she needed to tell him what happened while she was stranded on the planet, it was no surprise to learn at the end of the episode that she’d been telling him everything over the course of the show. Still, it didn’t stop the final moments between Fitz & Simmons from being quite emotional – especially when Fitz decided he’d help Simmons get Will back. So what does all of this mean for FitzSimmons? Expect some struggles for the fan-favorite duo, especially as it’ll take some time to build a new portal to try and bring Will back.

Now that Fitz knows about Will, what does this mean for FitzSimmons’ relationship going forward?

It puts a pin in their relationship for sure. Time is of the essence and they don’t have time to dissect how they feel right now. They’re focusing on getting Will back and doing the right, humane thing. The fact that Fitz is willing to help means there is still hope for their relationship. Whether that can ever be romantic now, I don’t know. We’re going to see them struggle with that, because Jemma never stopped loving Fitz. She just felt like she was never going to see him again. Her feelings never went away, but she now has feelings for another dude. It’s an impossible situation for everyone. It’s creating some brilliant scenes for Iain and I to have together.

How long will Fitz and Simmons be working on building a new portal? Is this going to be a storyline that pays off sooner rather than later, or is this going to be a slower burn?

It’s going to take a while. There’s a lot going on at SHIELD right now. And who knows if it is even going to work when we do eventually think we’ve found a solution.

As for whether or not Simmons has other reasons for going back to the planet, Henstridge made it clear that Will is her only reason for wanting to reopen the portal.

CBR News: Just how desperate do you think Simmons is to rescue Will, and does she have any other motives for returning?

Elizabeth Henstridge: No, he’s the sole motive. I think she doesn’t want to see that planet ever again and the fact that we don’t know what It is — It’s killed everybody else apart from Will and Simmons, so going back is extremely dangerous. Honestly, I think she’s tried to compartmentalize it, like, “Well, that was then, now I’m back and I need to concentrate on being back” and she just can’t. She can’t live with herself without trying to get him back to safety because he saved her life. Will is her sole focus right now.

Agents of S.H.I.E.L.D. airs Tuesday on ABC at 9 PM EST!

Sources: Entertainment Weekly, The Hollywood Reporter, and Comic Book Resources.