How did Eleven open the gate in season 4

• Warning: Major spoilers ahead for "Stranger Things" season four.
• The new season of Netflix's show includes flashbacks to events, spanning from 1959 to 1986. 
• We've put all the new major events into chronological order with important scenes from past seasons.

The first season of "Stranger Things" told the story of secret government experiments on children gone wrong. Various kids were born with supernatural abilities, and imprisoned in the Hawkins National Lab (HNL) for testing.

When Eleven, an 11-year-old girl with "011" tattooed on her wrist, escaped the HNL in 1983, she encountered a group of boys who were looking for their friend Will, a fellow preteen who had been taken into an alternate dimension known as the Upside Down.

But now, in season four of the Netflix series, the timeline of events has been expanded all the way back to the 1950s. New scenes explained how and why Eleven accessed the Upside Down while inside the HNL.

With the following timeline, we break down exactly how the new villain in the Upside Down (Vecna) was created — and why he's been haunting Eleven and Hawkins since 1979. 

Note: Events marked with an asterisk (*) have been estimated based on context clues within the show.

*1947: Henry Creel is born shortly after his father, Victor, returned from fighting in World War II.

We know from newspaper articles that Nancy and Robin found that Henry Creel was 12 years old when he killed his mother and sister, framing his dad for the gruesome murders in 1959. 

That means he must have been born sometime around 1947, a couple years after WWII. Victor Creel was a soldier, haunted by a bombing he ordered on a family's house somewhere in Europe. 

1959: Twelve-year-old Henry Creel murders his mother and sister. Henry's father Victor is imprisoned for the crimes.

As he later confessed to Eleven, Henry (AKA "One" or "Vecna") realized he had psionic powers (telekinesis, mind-control, the ability to make people see visions) when he was a young boy.

By the time he was 12, his mother had decided to call Dr. Martin Brenner to help figure out her son's strangeness. This enraged Henry, who later murdered his mother and sister using his supernatural abilities. 

The effort Henry spent using his powers to kill his family left him in a coma. His dad, Victor, was taken away to Pennhurst and convicted for the death of his family. 

But Henry hadn't died. Instead he had been secretly taken into Hawkins National Lab.

1959: Henry wakes up inside Hawkins National Lab under the care of Dr. Martin Brenner, who begins his experiments.

Henry told Eleven that Brenner didn't want to simply study his power — the doctor wanted to replicate them. 

So far "Stranger Things" hasn't revealed exactly how Henry gained his powers. One plausible theory is that something Victor did during the war (perhaps involving nuclear weapons or chemicals) led to his child's genetic anomaly. 

We know Brenner's team at the Department of Energy was trying to replicate Henry's powers by giving pregnant women drugs like LSD and leaving them in sensory deprivation tanks for long periods of time. 

Brenner started tattooing the children he held in captivity, beginning with Henry as patient 001 — or "One." 

*1972: Terry Ives gives birth to her daughter inside Hawkins National Lab, and Brenner "abducts" the baby.

Sometime in the early '70s, Terry Ives gave birth to her daughter, Jane. 

According to Terry, she woke up without a baby and was told she had miscarried. But Terry suspected the truth and went public with accusations that Dr. Brenner had "abducted" her child and was using her superpowers to fight the Russians. 

When Terry successfully broke into the Hawkins National Lab to try and find Jane, she was captured by Brenner's team and electrocuted until her brain function was all but destroyed.  

Jane was raised, along with the other children, by Brenner as number 011 — or "Eleven." 

*1976: Kali Prasad, or "008," escapes the lab.

As revealed in season two of "Stranger Things," only one child managed to escape Hawkins National Lab alive. 

That was Kali, known in the lab as "Eight." Her powers were centered on creative illusions, a skill that likely came in handy when she made it out of the lab. She fled to Chicago and started life as an outcast who hunted down former HNL workers and killed them for revenge. 

Though we don't know the exact year Kali escaped, we do know that she was no longer in the lab on the day Henry killed all the other children except Eleven. 

September 8, 1979: Henry plots the Massacre at Hawkins National Lab, and Eleven sends him into the Upside Down.

Henry, now in his early 30s, was forced to work as an orderly at HNL, assisting in the experiments and overseeing the other supernatural children. 

For whatever reason, he identified Eleven as the likeliest target for his manipulations and got her to remove a device Brenner had implanted in his neck. The device (called a "soteria," which we explained in our analysis here) had prevented Henry from using his powers or escaping the lab. 

Once the device was out, Henry set out to kill every last person inside the lab — including over a dozen children. 

When Eleven realized what Henry had done, she summoned an enormous amount of power and defeated the older man. Her psionic abilities were so advanced (even at the age of about 7 years old) that she opened a gateway between dimensions and banished Henry into the Upside Down. 

1979: After Henry's attack, Eleven loses her memory and knowledge of how to summon her strongest powers.

Brenner said that the massacre at HNL set Eleven back, shocking her system to the point where she didn't remember how to use her strongest powers or anything about Henry. 

In an interview with Variety, the Duffer Brothers also said that this is why Eleven's speech patterns changed from the 1979 flashbacks to herself in the early '80s. Her trauma was so intense that she even forgot how to form complex sentences. 

*1981: Eleven, now the only child left in HNL, tests her powers on soda cans, a cat, and in the Void where she spies on a Russian man.

As the Duffer Brothers explained in an interview with Variety, the Massacre at Hawkins Lab was so traumatic for Eleven that she effectively blocked out all memories from 1979 and earlier. That's why her grammar was so limited again, and we saw in flashbacks that she had to be re-trained to use basic powers. 

Brenner stopped trying to replicate the supernatural abilities on other children, making Eleven the sole test subject in the lab. 

She was able to enter into some sort of subconscious Void and listen to people speak and see some of their surroundings. The Department of Energy seemed to be planning on using Eleven to spy on Russians (and maybe even remotely assassinate them). 

But while she was in the Void one day, Eleven encountered a Demogorgon — one of the creatures who live in the Upside Down. 

November 6, 1983: Eleven escapes HNL and a Demogorgon begins hunting in Hawkins. Will Byers disappears into the Upside Down.

The first season of "Stranger Things" begins in 1983. 

Eleven was told by Dr. Brenner to "make contact" with the Demogorgon, possibly because he was keen to have her search alternate dimensions to find Henry again. 

When Eleven touched the Demogorgon inside the Void, she became so terrified that her powers burst out of her, and a Gate to the Upside Down was opened inside the lab. Somewhere among the chaos of the Gate opening, Eleven escaped HNL through the drain pipe Henry had shown her years ago. 

Meanwhile, the Demogorgon entered Hawkins and chased little Will Byers home. Will vanished into the Upside Down, and the Demogorgon continued hunting people in Hawkins. 

November 1983: Eleven befriends Mike, Dustin, and Lucas. In order to save them from the Demogorgon, she once again banishes the creature (and herself) into the Upside Down.

Eleven, who is now 11 years old in 1983, experienced life outside HNL for the first time when Mike took her in. 

After defeating the Demogorgon (which may have been acting on Henry's orders), Eleven vanished inside the Upside Down and then escaped — eventually going to live with Hopper in a secret cabin in the woods. 

*1984: In the alternate dimension, Henry discovers the special particles and forms the Mind Flayer.

In the season four finale, Henry monologues to Eleven about what happened to him after she used her powers to transport him into a new dimension. 

"I saw so many things," Henry told Eleven while recounting his exploration of the new realm. "And one day, I found the most extraordinary thing of all. Something that would change everything. I saw a means to realize my potential. To transcend my human form. To become the predator I was always born to be." 

Henry had become interested in spiders at a young age.

"Like me, they are solitary creatures and deeply misunderstood," Henry said in episode seven of season four. "They are gods of our world. The most important of all predators. They immobilize and prey on the weak, bringing balance and order to an unstable ecosystem."

So Henry took inspiration from the spiders, and created a shadowy monster that the Hawkins teens call the Mind Flayer.

June 28, 1984: The Russians test their prototype gate-opener.

The third season of "Stranger Things" starts off with a scene in Russia. This sequence happened in the summer of 1984 — it was a flashback to what was happening before the main events in season two, which took place in the fall of 1984. 

This machine test fails, but we know the team of scientists continued working on their secret project and moved to Hawkins to set up a new laboratory while all the events of "Stranger Things" season two were taking place.

The Russians likely learned about the possibility of opening inter-dimensional gates during their spying on the US Government as the Cold War was underway.

October 1984: Henry begins haunting Will Byers, this time with the Mind Flayer.

Throughout season two, we see the Mind Flayer target Will for possession. Henry wants the Gate to stay open and expand, so he can send more and more creatures (like demodogs and Demogorgons) into the dimension where Eleven is now hiding at Hopper's cabin. 

November 1984: Eleven uses her superior powers to once again defeat Henry and close the now-enormous Gate located at HNL.

After reuniting with her sister Kali and learning how to expand her powers, Eleven returned to Hawkins to save her new friends and family from the Mind Flayer.

She seals the Gate, though a small part of the Mind Flayer was trapped in her dimension (the piece that had possessed Will throughout the season). 

December 1984: Eleven and the other kids attend the Snow Ball, but Henry is keeping a watch on them through the Mind Flayer in the Upside Down.

As the season of "Stranger Things" closes with a winter dance at Hawkins Middle School, we saw that the Mind Flayer (and therefore Henry) is still watching Eleven through dimensions. 

July 1985: Henry once again terrorizes Hawkins using the Mind Flayer, and "bites" Eleven (causing her to lose her powers).

The small piece of the Mind Flayer that was left in Eleven's dimension managed to accumulate a physical body made out of exploded rats and humans. 

Henry (again, through the Mind Flayer) possessed Billy Hargrove and terrorized Eleven and her friends as he's determined to find and kill her. 

A Gate had been opened once again in Hawkins, this time by the Russians who had infiltrated the town and built a secret lab. Hopper and Joyce figured out how to close the Gate by shutting down the Russian machine. 

Meanwhile, the Mind Flayer had managed to injure Eleven by "biting" her leg and leaving some of itself behind. 

"I sought a means to open my own doors," Henry said in the season four finale. "I sought your power. So don't you see? Once again, you have freed me." 

So the Mind Flayer's "bite" in season three somehow helped Henry strengthen his own powers, enabling him to begin the murder spree we see later in season four. 

October 1985: Eleven and the Byers go into hiding in California.

Determined to get a fresh start for Eleven and the rest of the Byers family, Joyce moves out to California.

Eleven starts living as "Jane Hopper" — taking the first name her mother gave her and the last name of her adopted dad, Jim Hopper. 

There Eleven starts high school and improves her grammar. But her powers were still frustratingly gone. 

March 21, 1986: Henry kills Chrissy and begins hunting other teens in Hawkins.

At the start of season four, "Stranger Things" brings us to the spring of 1986 — nearly seven years after Eleven banished Henry into the Upside Down. 

Once again plotting a way to get to Eleven and take over her dimension, Henry begins haunting and murdering select teenagers in Hawkins (Chrissy, Fred, and Max to start). 

This is the first time we see what Henry looks like after so many years inside the Upside Down. He can physically tether himself to the "hive mind" of the Upside Down, and use his telepathic powers to make victims see visions and transport their subconscious into the Upside Down where he rules. 

March 1986: Eleven undergoes a special procedure to help her recall her memory of Henry so she can re-access her powers.

Once again under the guidance of Dr. Brenner, Eleven (now about 14 years old) uses the NINA system to re-live her memories of HNL. She's finally able to remember being a younger girl and how she fought and defeated Henry. Her powers return. 

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