“Marvel’s Agents of S.H.I.E.L.D.” Season 3, episode 5 is all about survival. The episode takes viewers back in time to look at Simmons’ (Elizabeth Henstridge) six months trapped on another planet. Simmons is the focus of the hour, which emphasizes just how terrible life was for her. This hour of the ABC drama also explains why she needs to return to the planet.

An Optimistic Beginning: This episode starts six months ago when Simmons and Fitz (Iain De Caestecker) agreed to go on a date, but then the scientist was absorbed by the portal. She records all of her observations on her phone. She can figure out that she is in a different solar system, but there is no one around to ask what this place is. She waits in the location where she arrived, hoping that help is on the way.

Eventually, she has to leave the portal location to find food and water. As she walks, she contemplates her date with Fitz to make the time pass. She worries about what she’ll wear, if they’ll run out of things to talk about. She gets caught in a sandstorm and gets knocked out, but she just gets back up again when she regains consciousness.

Simmons finally finds water and, since it’s a desert on this planet, she goes for a swim. However, she is attacked by a plant in the water that tries to pull her under. Days later, she realizes that it is her only viable source for food. She faces the alien plant and kills it.

She continues to record messages for Fitz on her phone (which apparently has an incredible battery because Fitz engineered it). However, she is starting to sound less optimistic about her rescue.

The Astronaut: Simmons falls through a trap while exploring and ends up underground. She wakes up in a cage and believes that she is being held hostage. A man (Dillon Casey) gives her food and water through a slot in her cage, but he doesn’t tell her much.

Eventually, Simmons escapes by pretending she is sick. She knocks him on the head with a bowl but she falls and gets a cut on her leg. “Kill me if you want, but I’m not going to be your prisoner,” she says. Instead he helps her with her wound.

Suddenly, he has to save them from a sandstorm. Once they’re underground, he reveals that he fears the sandstorms and believes that there is a monster that comes with them.

The man also explains that he was keeping Simmons in a cage because he didn’t think she was real. He finally introduces himself as Will and says that he was stranded on a mission for NASA in 2001. She finds out that Will was with a team that NASA sent through the monolith.

“It has this was of getting inside your head and making you crazy,” Will says of the sandstorms. Two of his team members killed themselves. The final teammate attacked him and Will had to kill him. Simmons tries to reason that it might not be the planet or the sandstorms, but the isolation that drove them mad. Will says that she doesn’t understand.

Simmons declares that they’re going to work on a way to get home, whether he believes in it or not. “I’ll be the voice of hope, you’ll be the voice of doom,” Simmons tells him.

The Escape Attempt: While collecting food, Jemma goes into Will’s “no fly zone” where she finds the remains of someone else. There is a sword, wine and, most importantly, a sextant. Once she sees the sextant, Simmons realizes that she needs to look at the stars.

She could fix an old NASA machine to determine how fast the planet is rotating and predict where the portal will next appear. They use her phone to power one of Will’s old NASA computers. The cell phone eventually dies, but Simmons gets one estimate out of it. She thinks the portal will next appear in the middle of Will’s “no fly zone.” The monstrous sandstorms happen often there and they’ll have to cross a small canyon, so he isn’t thrilled. However, he has to take his chance.

When they get to the canyon, it’s suddenly larger than when Will was last there. It would be impossible to cross in time, but Simmons prepared a message in a bottle just in case. The bottle misses the portal by a second and smashes on the ground.

“We’re never going home,” Simmons says. She breaks down crying and tells Will that he was right, there’s no hope on this planet.

“That’s what I used to think. Then you showed up,” Will said. Emotions are running high and Simmons doesn’t think she’ll ever see anyone else ever again, so they kiss.

A few weeks later, it’s clear that the two are in a romantic relationship. After all, it looks like they’re spending the rest of their lives together. They sit on the top of a cliff to see a moment of a sunrise. Jemma says it’s the only one they’ll see for 18 years.

While they’re waiting, she sees a flare. She believes it’s Fitz and runs toward it. Then a sandstorm starts and she sees an astronaut. She thinks it’s NASA, but Will says to run. She starts to get away, but she loses Will. Simmons hears a gunshot, but she doesn’t know what happened. Once she hears Fitz’s voice, she has to go toward him.

Present Day: “I never would have survived without him,” she tells Fitz. She is explaining to him why she wants to find a way to return to the awful planet.

Fitz goes off to the lab and Simmons asks him to talk to her. He is pulling up plans on the computer. “We’re going to get him back,” Fitz says.

In the final scene, viewers see Will is still alive and completely alone.

“Marvel’s Agents of S.H.I.E.L.D.” Season 3 airs Tuesdays at 9 p.m. EST on ABC.