Full of '80s nostalgia and a plethora of sci-fi/horror homages, Netflix’s Stranger Things was one of the biggest surprise hits of 2016. The Duffer Brothers created a show that perfectly encapsulated what growing up in the '80s was like, at least from a cinematic standpoint. Amid going to school, riding your bikes outside, and playing arcade and board games with your friends, there was always the possibility of something strange in your neighborhood.

It was easy to get hooked on Stranger Things because it had an immediate mystery that needed to be solved (What happened to Will Byers?), only that mystery was shrouded in multiple layers of an even bigger, deeper mystery (What exactly is the Upside Down and how is Eleven connected to it?). Essentially it was a mystery sandwich that still has pieces of it that remain intact, despite wrapping up a few things by the end of season one.

Now, with Stranger Things 2 premiering just around the corner on October 27th, we can’t help but wonder if any of those unsolved mysteries will get an explanation. There are still a ton of questions that need answering, although it’s unlikely we’ll get closure on everything.

As we prepare to revisit the story of Eleven and all our other friends in Hawkins, Indiana, it’s time to explore the 15 Unresolved Mysteries and Plot Holes That Season One Left Hanging.

15. Where is Eleven?

As soon as we saw Hopper leave those Eggos in the woods, it was obvious we hadn't seen the last of Eleven. She still exists in some capacity— in some dimension— possibly within The Upside Down or another layer of that universe.

Judging from the fact that Millie Bobby Brown is listed as appearing in all nine episodes of season two, we'll probably see Eleven pretty much right away. Whether it's through flashbacks or glimpses into where she's been trapped, remains to be seen. However, since she was the one who caused the tear in reality to form, she'll probably have a big role to play in fixing it.

There's a bigger, badder monster in season two— a "shadow monster" better known as the Thessalhydra, so it's definitely going to take a lot more power to take down something that large. But, for all we know, Eleven could actually be the monster, since we do hear a voice whispering Will's name in the season two trailer. That would sure complicate things, especially for poor Mike who can't seem to get her out of his head.

14. Why did the Demogorgon choose to take Will when he wasn't bleeding?

One of the most irksome plot holes we just need to have resolved in season two involves the Demogorgon’s reason for taking Will. It was established throughout the show that the monster was attracted to blood— hence why it took Barb and how Jonathan and Nancy got it to appear for them— but that rule didn’t apply to Will.

He first encounters it in the middle of the road by Hawkin’s Lab. It then proceeds to follow him to his house and into the shed where he’s taken into the Upside Down. Was it just a matter of wrong place, wrong time, but then why did it linger around his house—hunting him?

Does he have something the other boys don’t? Joyce does mention that he’s a “sensitive kid.” Maybe that means he was more vulnerable to The Upside Down, or that he has untapped powers himself.

13. Is Will really Will?

At the end of season one, everything seems hunky dory until Will coughs up a nasty slug and sees The Upside Down appear momentarily in his bathroom. The season two trailer also shows Will having the same sort of flash while in an arcade with his friends. So did Will completely come back from The Upside Down or is part him still trapped there somehow?

Hopper and Joyce did come across a giant egg when they were looking for Will. That egg has appeared on a promo poster for the new season, referencing the original Alien’s movie poster with the tagline: “In The Upside Down, no one can hear you scream.”

Could Will now be a portal to The Upside Down, pulling all of Hawkins in there with him? Wouldn’t it be super creepy if everyone in Hawkins turned around at the same time with their eyes wide and mouth open— Invasion of the Body Snatchers-style— pointing at everyone who hasn’t been assimilated yet? Talk about nightmare fuel.

12. What is Eleven's connection to the Demogorgon?

Speaking of Eleven, many fans theorize that there's a strong connection between her and the Demogorgon, outside of making contact with it mentally. Its been suggested that the monster and Eleven are one in the same, or that her fear created it because of all the trauma she experienced as one of Dr. Brenner's experiments.

She even says to Mike, "I'm the monster," which everyone seems to just brush aside despite the fact she has a limited vocabulary and always chooses her worlds carefully.

It also can't be a coincidence that Dustin, Mike, and Lucas find Eleven in the same area they're looking for Will. The Demogorgon doesn't seem to venture too far away from Hawkins lab, seemingly tied to it by the opening created there when Eleven made contact.

Even if Eleven isn't literally the monster, she definitely has power over it and doesn't seem afraid of it unlike everyone else in the show.

11. Is Dr. Brenner really dead?

Seemingly the mastermind behind all the strange experiments going on at Hawkins Lab, Dr. Brenner (Matthew Modine) became a casualty of his own work at the end of episode eight. Or did he? We saw the Demogorgon attack him after it broke through the wall of the school, but did it actually kill him? We never saw a body.

Since the cameras cut away, it's entirely possible that wasn't the last we've seen of the character, even though a new doctor is supposed to be in charge of the lab in season two—Dr. Owens (Paul Reiser).

Modine made a cryptic post on Instagram saying, "More to be revealed, uncovered," and the Duffer Brothers have even said there's a possibility Dr. Brenner will return. Perhaps we'll see him in The Upside Down this season or maybe in flashbacks that reveal more of Eleven's origin story.

10. Are there (or were there) other children like Eleven?

Eleven’s name brings up a lot of unanswered questions, such as why the heck was she named that? If she was the eleventh experiment, where are one through ten? It’s possible that these were the other people seen in the photo of the Project MKUltra subjects, like Terry Ives, but they could have been other children as well.

There are certainly a lot of conspiracy theories on the internet claiming that the real MKUltra did experiments on children, so there may have been others before her or even coexisting in the lab without her knowledge.

Then there are the episode titles for season two. Originally, the name of the very last episode of the new season was called “The Lost Brother,” now only referred to as “Chapter 9.” Could Eleven have a brother, or perhaps a symbolic one in that he was a fellow experiment? Hopefully we’ll find out on October 27th.

9. What are they ultimately trying to accomplish at Hawkins Lab?

While obviously we know that the lab had been doing experimentation to study the effects of LSD on the mind, little is known on why and what their ultimate purpose was. Eleven’s ability to utilize radio frequencies in order to find Will shows that her brain’s electromagnetism has been altered so much that it can actually interfere with radio waves.

We saw Dr. Brenner using Eleven to spy on Soviet agents and somehow broadcast their speech from very large distances, but she also possessed telekinesis. She could crush a soda can with her mind and injure a living thing without lifting a finger.

So were they trying to turn Eleven into some sort of super soldier or weapon against the Soviet Union? Maybe, or they could have been prepping her to communicate with an enemy that was a lot farther away—perhaps something lurking in space or another dimension—which is why Dr. Brenner encouraged contact with the Demogorgon in the first place.

Either way, they were most likely trying to figure out how to use the mind as an energy source, possibly to effect or change reality.

8. What's going to happen to the other people who went in The Upside Down without protective gear?

Besides Will and Barb, who were both taken into The Upside Down unwillingly, other people have been inside it as well. Nancy went in while searching for whatever took Barb, as did Hopper and Joyce who took off the helmets of their hazmat suits once they found Will. Dr. Brenner warns the latter two that the air in The Upside Down is toxic, so what will happen to all those exposed to it?

We never got to see how they arrived at the conclusion that the air was poisonous, but we’re guessing it wasn’t pretty. One lasting effect seems to be a visual connection to the world, at least on some level.

In the season two trailer, we also see Will having tests done on him—possibly back up at Hawkins Lab—so he was likely physically as well as mentally affected by The Upside Down. Hopefully, it won't cause everyone to turn into monsters, but we wouldn't rule anything out as a possibility at this point.

7. Who is Eleven's father?

It seems safe to conclude that Terry Ives is Eleven's mother, but then who is her father? Dr. Brenner has Eleven call him "papa," which may just seem like a matter of convenience rather than affection, but he does seems to care about her on some level.

Let's look at the facts here. Terry Ives was unknowingly pregnant while undergoing her experimentation, which means it probably happened during the same time. It's very possible that she had a sexual relationship with Dr. Brenner, which would give him a stake in the baby's future and a motive for kidnapping her.

Sure the lab could have just wanted to see how the drugs had affected the baby's brain, but then why stage a hoax if they didn't feel like they had some sort of ownership of the child? Maybe Brenner even planned the whole thing in order to keep watch over his daughter and supervise her evolution. Stranger things have happened. See what we did there?

6. How did they explain to an entire town that Will wasn't really dead?

Seeing as how the people in Hawkins already thought Joyce Byers was off her rocker, how did she explain to everyone what happened to Will? In fact, how did any of the people who knew about Eleven, explain it to their loved ones (i.e. the Wheelers)?

Will was missing for several days. Hell, there was even a funeral for him. How do you come back from that as a community? You can't exactly explain away the fact that there was a body.

Since Hopper seemed to have made some sort of deal with the lab/government in order to look for Will in The Upside Down, he was probably instructed on what to say. Still, it's a pretty big plot hole to fill considering strange things are going to continue happening there in season two (although the opening scene reportedly isn't in Hawkins).

5. Who are Dustin's parents?

Although it's not a huge mystery like some of the other ones on this list, we can't help but wonder who Dustin's parents are. We see a lot of Mike and Will's families, and even Lucas' family at Will's funeral, but nothing of Dustin's.

In fact, he doesn't really mention them at all. Lucas at least shares that a bunch of the supplies he brings for Operation Mirkwood in episode three are from 'Nam, meaning they're his dad's, but all Dustin brings is food.

Dustin's parents do make an appearance in season one at Will's funeral, but they're not exactly easy to spot. This is the only picture of the three of them together, but we have no idea what kind of people they are.

Is Dustin ashamed of them? Are they nice to him? Will they ever become an integral part of the story? Dustin is one of the most lovable characters on the show and it would be nice to find out a little of where he came from.

4. What's Hopper's story?

Another character whose origins we could do to explore further is Jim Hopper. His past his its own share of mystery and missing pieces. We know he lived in the city for a while with his wife and daughter— and that his daughter, Sara, died from what was supposedly childhood cancer— but even that isn't completely confirmed.

According to David Harbour's reddit AMA, Sara's actual cause of death is "a secret we may explore in s2." Could she have been one of the Hawkins Lab experiments and was actually adopted by Hopp and his wife?

We also don't know much about his time growing up in Hawkins. In Harbour's AMA he did confirm that Hopper and Joyce Byers dated in high school, but we don't know the extent of their relationship. Lonnie does allude to a beef with Hopper when Jonathan goes to visit him, so does that mean they had a love triangle like Nancy has with Steve and Jonathan? We need answers.

3. What was the deal Hopper made with the Hawkins Lab/CIA?

We're all curious to know just what kind of deal Hopper made with Hawkins Lab and the CIA. They could have just killed him like they did Benny the burger guy. He obviously proved to them that he knew too much, but also that he was indispensable when it came to giving them what they wanted and doing the dirty work. Perhaps there was more to it than that, though.

Judging by how a car came to pick him up in the last episode, it's very possible that he now works for the government in some capacity. After all, he knows that Eleven is still alive somehow since he left her food.

That box was probably put there by Hawkins Lab, or he was instructed by them to leave it there. It's probably made of something that's able to transcend multiple universes, which may prove to be important in the upcoming season.

2. What is The Upside Down and is it the only alternate dimension?

The Upside Down remains one of the biggest unsolved mysteries in Stranger Things, but what exactly is it? An alternate dimension? A future Hawkins? Hell on Earth? Whatever it is, monsters roam freely there, and have essentially taken over where humans left off.

Fan theories abound, speculating that The Upside Down is Hawkins after a nuclear explosion meant to decimate the monsters that took over. Then all of those white particles in the air are actually fallout, which would also explain why it would be toxic to breathe. That's certainly a legitimate explanation, but what about the rest of the world?

The Upside Down can't only exist within Hawkins; the gate was just opened there. So do other dimensions-- both malevolent and benevolent exist-- where things are all just a little bit off in comparison to their reality? We may not get a direct answer to what The Upside Down is in season two, but hopefully we'll at least come to understand it a little better.

1. What's the connection between The Upside Down & Electricity?

In almost every episode of Stranger Things' first season, we saw a strong connection between The Upside Down and electricity. When the Demogorgon, or someone else who was stuck in The Upside Down were near, the lights would flicker in response to their presence.

Traditionally— in horror movies— lights flicker in response to a paranormal entity, something from the spirit world. Similarly—in sci-fi films—lights and electronics go haywire when aliens approach, such as in the case of a UFO abduction.

While it's unclear whether the Demogorgon was supernatural or alien in origin (if either), it is clear that Hawkins Lab was aware of this connection with electricity. After all, they were operating under a Water & Power front.

In theory, someone with strong telekinetic powers like Eleven would basically be like a electrical superconductor who could control physical matter by influencing its energy. However, it still doesn't explain why there was electricity in The Upside Down, unless it was getting its power from somewhere in our world (i.e. Eleven or Hawkins Lab).

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What are some other mysteries and plot holes that need to be answered in Stranger Things' season two? Sound off in the comments!