Of all the various properties that comprise the Marvel Cinematic Universe – that’s 12 movies, five short films, and four television series at present – few have proven to be as central to the shared universe’s overarching storyline as Agents of S.H.I.E.L.D. The inaugural Marvel TV show just finished the first half of its third season two nights ago, capping off a 10-episode run that has done much to help set the stage for next year’s Captain America: Civil War (the first entry in Phase 3) and all the films beyond, going all the way up to 2019’s The Inhumans (Phase 4’s first installment).

If you don’t watch Director Phil Coulson (Clark Gregg) and his team on their weekly adventures to rebuild S.H.I.E.L.D. as a leaner, meaner, more secret agency, it’s understandable. The sheer amount of time that the MCU now requires in order to fully follow along means that even people who are caught up on all the movies might be left out on what’s happening in Agents of S.H.I.E.L.D., Agent Carter and Netflix shows Daredevil and Jessica Jones. But that’s why we’re here – to provide the basic information you’ll need moving forward to appreciate the full background and connective tissue of the company’s ever-more-climatic narrative.

We have compiled for you What Marvel Movie Fans Need to Know from Agents of S.H.I.E.L.D.’s Season 3.0 – and though there are only four points, they are all doozies. They’re all also SPOILERS, so please proceed carefully if you plan on watching the mid-season finale.

1. The spread of the Inhumans

Ronan The Accuser Guardians of the Galaxy Agents of S.H.I.E.L.D. Season 3: What Marvel Movie Fans Need to Know

Across the show’s first two seasons, it was revealed that the Kree, the alien race first seen on the big screen in 2014’s Guardians of the Galaxy (that’s Ronan the Accuser’s species), visited Earth several millennia ago for the express purpose of creating a slave warrior race that could be used as foot soldiers in the Kree Empire’s never-ending battles for interstellar conquest. The would-be alien rulers ultimately thought better of this plan, however, and decided to exterminate all of the “abominations” – although a number of these genetically-modified, superpower-fueled humans managed to live on in secret and have progeny.

This lineage continues on to the present day, and though these descendants call themselves Inhumans and loosely organize themselves into various communities, most have yet to undergo Terrigenesis, the process that activates their latent super powers and which requires a Terrigen Crystal to initiate.

This all changed in the Agents of S.H.I.E.L.D. season 2 finale (which aired in May 2015, just two weeks after The Avengers: Age of Ultron released). During a skirmish between Coulson’s team and a particularly militant group of Inhumans, a box of Terrigen Crystals got pushed off of a vessel and sunk to the bottom of the ocean floor, leaking its contents – which eventually get consumed by fish, which, in turn, get processed into fish oil pills and distributed around the world.

Although SHIELD is eventually able to track down the source of this Kree contaminant and discontinue most of the pills, computer simulations show that it’s had an irrevocable, exponential effect on the (In)human population: soon, there will be countless newly-activated superpowered individuals on the move, confused as to the nature and origin of their powers and unpredictable in their responses – will they identify more as human or as alien? If this sounds suspiciously close to the X-Men franchise, that’s because this is essentially Marvel Studios’s workaround.

2. Continuing Sokovia backlash

sokovia accords what marvel movie fans need to know Agents of S.H.I.E.L.D. Season 3: What Marvel Movie Fans Need to Know

Audiences may first have learned of the public outcry over the Sokovia incident in last July’s Ant-Man, but the full effect of the controversy is laid bare in the first few episodes of Agents of S.H.I.E.L.D.’s third season.

It makes sense for such a prolonged furor – after all, the human race nearly went extinct when Ultron scooped Sokovia out of the Earth and attempted to imitate the asteroid that killed off the dinosaurs. Even if it hadn’t been a near-extinction event, it still was a city floating several miles in the sky, an occurrence which is sure to raise an eyebrow or two. But beyond being a nice touch of realism in a superhero-infused world, it also serves double duty as being a deft bit of foreshadowing: it is Age of Ultron’s climax, after all, that serves as the foundation for the titular conflict in next summer’s Captain America: Civil War. All S.H.I.E.L.D. is doing is helping to reinforce that foundation.

It also manages to expand on the show’s ever-building narrative momentum, saying that the recent rash of Inhuman “births” has only added fuel to the fire of public hysteria. With superheroes on the one side and super powers on the other, the average populace is feeling increasingly caught in the middle – so much so that President Matthew Ellis (originally introduced in Iron Man 3) has to personally introduce a brand-new initiative meant to deal with such crises in the future: the Advanced Threat Containment Unit. His primetime speech to the American public is revealing enough (and well-written enough) to warrant quoting in full here:

“By executive order, I have created a special task force to neutralize these alien threats on our soil. The Advanced Threat Containment Unit, or ATCU, will be given full license to act with whatever authority is necessary. The laws of nature have changed – and until the laws of man change to reflect that, we must do what we feel is right.”

It’s unknown whether the ATCU survives as a fully functioning unit going into season 3.5 – most of its core personnel have been killed, and the initiative is revealed to be a pet project of Hydra’s – let alone heading into Civil War, but we do know, of course, that the law will, indeed, end up changing in that next film, when the Sokovia Accords go into effect.

3. The rise – again – of Hydra

gideon malick what marvel movie fans need to know Agents of S.H.I.E.L.D. Season 3: What Marvel Movie Fans Need to Know

Grant Ward (Brett Dalton), one of the original members of Director Phil Coulson’s team, has had quite the wild ride for a character arc. After being outted as a Hydra plant at the end of the first season, he spent the entirety of season 2 attempting to build a new identity for himself away from the auspices of either S.H.I.E.L.D. or Hydra, and has now, in the third season, finally found a direction and purpose for his wayward life – the assassination of Coulson and the eradication of his core group of agents. Why? It’s a long – and convoluted – story, but it revolves around that oldest and most primal of human motivations: revenge.

The result has been the concerted effort of not only rebuilding Hydra, which had been toppled last year due to the twin efforts of the Avengers (taking down Baron Wolfgang von Strucker at the beginning of Age of Ultron) and Director Coulson’s S.H.I.E.L.D. (taking down all the other leaders), but at re-establishing it as the mirror image of S.H.I.E.L.D., with Ward bestowing on himself the title of director. In his efforts to remake the terrorist organization in his own image, Ward goes after Werner von Strucker, the good baron’s son, in the hopes of raiding the von Strucker family’s legendary, endless vaults, at the least, and of training Werner as an agent at long last, at the most.

The move fails to succeed on either count, but it does successfully get the attention of the only other remaining Hydra power player: Gideon Malick (Powers Boothe), who was first seen as a World Security Council member in The Avengers and who is now revealed to be one of President Ellis’s top advisors. With access to the von Strucker riches and a hand in nearly every important government agency – including the Advanced Threat Containment Unit, which was created at his recommendation – it is Malick who is the real guiding hand behind Hydra’s continued existence.

This is especially true when Coulson and Ward finally have their long-awaited faceoff in the mid-season finale, with Coulson coming out the victor – and crossing the moral line of single-handedly (literally) killing his former teammate. This leaves Malick as the sole standing head of Hydra… for now, at least.

4. Hydra’s real purpose

hydra logo what marvel movie fans need to know Agents of S.H.I.E.L.D. Season 3: What Marvel Movie Fans Need to Know

What makes Malick such a threatening force to be reckoned with goes well beyond his influence with the government and goes to his high standing within Hydra itself – he is one of the few individuals on the face of the Earth who is aware of the organization’s true origins.

Rather than being an offshoot of Nazi Germany’s SS, as was detailed in Captain America: The First Avenger, Hydra places its beginning several thousand years before that, presumably to some time shortly after the Kree finished their inaugural human experiments. One Inhuman emerged from Terrigenesis with such incredibly strong powers, he appears able to manipulate others’ perceptions as well as matter itself (making him like The Avengers: Age of Ultron’s Scarlet Witch, but to the nth degree). He can also inhabit dead individuals’ bodies as some type of animating force, which is precisely what he ends up doing to the defeated Ward. With such abilities, the rest of humanity immediately feared that he would dominate the entire planet, so they did the only logical thing: they banished him to another planet, using a Monolith of unknown origin that doubles as a portal.

A group of individuals (whether Inhuman or “normal,” we do not know), however, saw benefit in having the chaos that is apparently inherent in mankind be tampered down by an iron fist, and they conspired to return the most powerful Inhuman Earth has ever seen. They started an ancient society that would take volunteers and send them through the portal, though none has ever successfully returned; history would mistakenly record these rituals as blood sacrifices and assign them to paganistic origins. Over the millennia, this society would change its name and its emblem, but its true purpose never wavered, and its insignia would bear remarkably consistent visual elements, until it reached its modern identity during Adolf Hitler’s reign: Hydra, the multi-tentacled entity with the death skull as its singular head.

Where the organization goes now, with the long-banished Inhuman back on Earth and, apparently, ready to claim Hydra as his own personal army, is unknown. But given that both Brock Rumlow, a.k.a. Crossbones (Frank Grillo), and Baron Zemo (Daniel Bruhl) are both scheduled for an appearance in Captain America: Civil War, it would seem that Hydra is still standing strong in one form or another come next summer.

In the meantime, however, it’s worth pointing out that this switch in Hydra’s intent and purpose replaces, in one single stroke, the Captain America films as the central-most pillar of the Marvel Cinematic Universe with Agents of S.H.I.E.L.D., fundamentally changing the skeletal structure of Marvel’s meta-franchise and easily being the biggest revelation that the show has managed to unleash on Marvel movie fans across its 54 episodes to date.

Agents of S.H.I.E.L.D. returns Tuesday, March 8th, 2016 at 9pm on ABC.