Stranger Things season 5 volume 2 ending explained: What actually IS the Upside Down?

Warning: Major spoilers ahead for Stranger Things season 5 volume 2.

The dramatic arrival of Stranger Things season 5 volume 2 has made a few things very clear: Vecna (Jamie Campbell Bower) is growing stronger, our heroes are in more danger than ever before, and the entire Wheeler family only deserves good things after this absolute nightmare.

Episodes 5 to 7 of the hit Netflix sci-fi are officially here and, with just the finale left to go, the show's creators, the Duffer Brothers, have answered plenty of questions while teeing up the very last battle for Hawkins.

The new episodes see Sadie Sink's Max return to her body after being imprisoned in Vecna's mind. Meanwhile, Nancy (Natalia Dyer) and Jonathan (Charlie Heaton) nearly die in the Upside Down, Dustin (Gaten Matarazzo) casually figures out exactly what the Upside Down is (a question we've been asking for nigh on a decade), and Will (Noah Schnapp) finally has his big moment. Oh, and Karen Wheeler (Cara Buono) saves the day yet again.

Every single character will have a huge part to play in what comes next but, while we're waiting for the finale, here's your breakdown of exactly what happened in season 5 volume 2.

Stranger Things season 5 volume 2 ending explained: What actually IS the Upside Down?

Buckle up, nerds. We've got Dustin to thank for this explanation. The Upside Down is an unstable inter-dimensional bridge, or a wormhole, that rips through space and time, held together by exotic matter and connecting Hawkins to another world, the Abyss.

Dustin theorises that everything they've faced in the Upside Down (the Demogorgons and the Mindflayer etc) truly originated in the Abyss.

It's where Eleven (Millie Bobby Brown) previously banished Henry but, since Dr Brenner (Matthew Modine) forced her to make contact with him in the Abyss, the bridge formed - and Vecna and his minions have been using it ever since to return to Hawkins.

So the Upside Down is not, as we previously assumed, another dimension in itself. That means the true challenge is not just cutting off the bridge, but destroying the Abyss once and for all.

What's Vecna's plan and why does he need the kids?

Vecna wants to merge the Abyss and Hawkins, but he needs the children to amplify his abilities.

He believes he can use the 12 children he's kidnapped, including Holly (Nell Fisher) and Derek (Jake Connelly) as "vessels" to amplify his powers, due to his belief that they are weak and can be easily controlled.

During his time away, Vecna was building rifts and weakening the Abyss like he weakened Hawkins, so that when the two collide, they will become one.

So, as Mike (Finn Wolfhard) lays out, the plan to fight him just got a whole lot more complicated. The gang need to get 2,000 feet in the air, get into the Abyss, free Holly and the children and kill Vecna.

Oh, and Dustin's little addition - set off a bomb in the Abyss to destroy it forever. Easy!

How did Max escape and what happened to Holly?

Max (Sadie Sink) escaped her imprisonment in Vecna's prison through his most traumatic childhood memory, with the help of her connection to Lucas in the outside world.

While Vecna comes after them, Will temporarily inhabits his body, slowing him down and telling Max and Holly to run.

But Holly is unable to fully escape Vecna's clutches, and is forced to return to his mind prison, with Vecna manipulating the rest of the children into believing Max is a monster.

After searching Henry's most traumatic memory, the cave, Max and Holly see a young Henry stumble upon a scientist, clutching a briefcase, who appears to believe that Henry has been sent to hurt him.

The scientist shoots Henry in the hand and, in a bid to save himself, Henry hits the scientist repeatedly with a rock, eventually killing him. While Max tries to pull Holly away, the youngest Wheeler sibling witnesses Henry opening the briefcase (although she doesn't see what's inside - more on that in a moment).

Around the corner in the cave, Max and Holly find their way out. Max sees Lucas on the other side but tells Holly she has to find her own way out. After a pep talk from Max, which sees her remind Holly of how strong she is, and helps her to find her connection to the outside world through her Holly the Heroic pendant, Holly finds her way out too.

Max believes Holly will wake up in the Upside Down and promises to find her there if she heads to its version of the Wheeler house, and the pair go their separate ways.

But, as Dustin realises, Holly isn't being kept in the Upside Down - she's in the Abyss. She wakes up and finds herself and the other children attached to the vines in the Abyss, just like Will was. After freeing herself, she makes a run for it, with Vecna following closely behind her.

In a stroke of good luck, Holly trips over and sees part of the ground light up - a gate to the Upside Down. Steeling herself, she pushes herself through it and starts to fall thousands of feet to the ground in the Upside Down. Nancy, who has narrowly escaped death there after shooting at the exotic matter, hears her screams and races to find her - only to see her sister hovering in the air and being pulled back into the Abyss by Vecna.

Vecna takes Holly back into his mind, convincing the other children that Max is a monster and has manipulated Holly. While Holly attempts to escape again, she fails, and episode 7 ends with Henry placing the children into a trance and executing the final part of his masterplan.

What was in the briefcase in Henry's memory?

Warning: Spoilers ahead for Stranger Things: The First Shadow.

This has only been teased thus far in the series, but the stage play Stranger Things: The First Shadow reveals that Henry grew up near those caves in Nevada. On the day he entered the caves and found the scientist, he discovered technology that transported him to Dimension X.

While he was there, he encountered the Mind Flayer for the first time, which transformed him for good and turned him into the villain we know and hate.

No doubt, the cave is going to play more of a role in the finale episode.

What's going on with Eleven and Kali?

Volume 2 also sees Kali (Linnea Berthelsen) recount the horrors she saw in Dr Kay's (Linda Hamilton) lab before Eleven and Hopper (David Harbour) rescued her. She recalls seeing countless pregnant women, who Kay infused with Kali's blood in an attempt to restart Brenner's programme.

But that makes her realise that Kay will never stop hunting Eleven and Kali for their blood. In her view, the pair of them will never be free. While Mike attempts to convince Eleven that they could kill Kay or escape to a faraway place, Kali convinces her that they'll find her, kill Mike and everyone she loves, and, using her blood, they'll create more children who will suffer, and more worlds.

So, as episode 7 ends, Kali comes up with a plan, which she thinks is the only way to stop the vicious cycle - a suicide pact. She tells Eleven that, when the plan to kill Vecna and destroy the Abyss works, the pair of them should stay on the bridge and, when the Upside Down vanishes, they'll vanish too.

Eleven now has a big choice to make - and whatever she decides will change the course of the world forever.

Stranger Things season 5's finale will be released on New Year's Day.

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