Since its debut as an offshoot of The Avengers, Marvel's Agents of S.H.I.E.L.D. has regularly reinvented itself. Along the way, it's tackled some major moments from the world of Marvel Comics, bringing to life heroes, villains, and plots that will likely never make it to the big screen. Season 4 of the show, however, took things to another level. The writers broke the season into three separate arcs that fed into one another and all paid off in the finale. By doing so, they not only kept things fresh, but opened the door for even more debuts from the comics.With much of season 2 and 3 of Agents of SHIELD focused on the Inhumans, season 4 took things in several new directions without abandoning the previous threads. After the loss of Lincoln and the destruction wrought by Hive in the season 3 finale, Daisy spent the intervening time off on her own and finally made the move toward becoming Quake. Coulson, meanwhile, gave up being the director of SHIELD and went back into the field as an agent. And while Mack and Yo-Yo remained in "will they, won't they?" mode, Fitz and Simmons appeared to be headed towards a solid relationship after year of build-up. From a character standpoint, the stage was already set for another stellar season of Agents of SHIELD”and then the writers upped the ante.Related: Sorry, Avengers Characters Won't Appear in Agents of S.H.I.E.L.D.

Ghost Rider

Thanks to San Diego Comic-Con last year, fans knew well in advance that Ghost Rider was finally coming to the MCU thanks to Agents of SHIELD. The show already introduced the Kree, the Inhumans, Quake, Mockingbird, Deathlok, and so many other major elements from the comics to the Marvel Cinematic Universe, but the Spirit of Vengeance was something else entirely. While some fans were disappointed that Johnny Blaze wasn't the Rider in question, followers of Robbie Reyes were more than happy to see the All-New Ghost Rider brought to life. And in the end, Blaze arrived as well.

The season kicked off with Coulson and Mack searching for Daisy, who spent her time away from SHIELD hunting the Watchdogs and gaining the name Quake by the press. Meanwhile, Jeffrey Mace was now in charge of SHIELD. After setting up the new status quo, the show jumps into a plot involving what looks like actual ghosts possessing people before they go insane and die. And unfortunately, May almost becomes one of them.

Each element of the first few episodes seems separate until everything starts aligning around Ghost Rider, the supposed spirits, and a mysterious book called the Darkhold. Essentially, Robbie's uncle Eli discovered the book when his coworkers used it to create a device that could generate both energy and matter. He attempts to take the book for himself while his boss puts a hit out on him. That attempt ends up paralyzing Eli's other nephew Gabe and killing Robbie. As fate would have it, however, Robbie is saved by a preexisting Ghost Rider who seems to be Johnny Blaze. He gifts Robbie the Spirit of Vengeance, saving his life and reworking the character's origin from the comics.

Eli then uses the machine that the Darkhold helped to build to turn his coworkers into the viral ghosts, whom only Robbie can destroy. After a stint in prison, he regains the Darkhold and uses the book and a new machine to grant him the power to create carbon. The device, and Ghost Rider's powers, however, seem to be tied to quantum physics and another dimension. Rather than creating matter, Eli is pulling it from another dimension, threatening the fate of the world. In the end, Robbie sacrifices himself to stop Eli and disappears until later in the season.

Throughout the first arc, we also learn of Senator Nadir who hates Inhumans despite having one for a brother. Quake rejoins the team and Mace is revealed to be an Inhuman operating as a hero named the Patriot. And all the while, Holden Radcliffe has been scheming and building the MCU's version of a Life Model Decoy.

LMDs

As the middle pod for Agents of SHIELD season 4, the LMD arc is built around the events from the previous story and is designed to set up the final one. While most of the agents were dealing with Ghost Rider and Eli, Radcliffe was slowly perfecting AIDA with the help of Fitz. Eventually, her presence is made known to everyone and she helps decipher the Darkhold and utilize its information to stop Eli. Unfortunately, all of that knowledge proves the final step in evolving AIDA into something dangerously powerful.

Though there's plenty of twists and turns and betrayals, it's eventually revealed that May has been replaced by an LMD and both Radcliffe and AIDA are responsible. They slowly infiltrate SHIELD while May is hooked into a simulation that keeps her occupied. As it turns out, that's actually Radcliffe's final goal.

Related: Agents of S.H.I.E.L.D. Season 5 Premiere Won't Include Fitz

Dubbed The Framework, the reality is one where a consciousness can live on even after the body has died. Radcliffe built it and AIDA for the woman he once loved, who just so happens to look exactly like the main LMD. Because she's dying, Radcliffe hopes to save her by putting her inside The Framework. AIDA, however, has been so corrupted by the Darkhold that she kills Radcliffe and places him in The Framework too before everyone but Daisy, Simmons, Yo-Yo, and a few lower ranking SHIELD agents get the same treatment.

The LMD arc continues the Watchdogs story, but they and Senator Nadir are eventually neutralized. We also learn that Mace isn't really an Inhuman, but was using a serum to appear strong and his supposed heroics during the events of Captain America: Civil War were all staged. There's a good bit of back and forth with Talbot and the Absorbing Man returning, but much of it doesn't have an impact on the final arc. Instead, Yo-Yo and the other agents watch as Daisy and Simmons hack into The Framework and attempt to save Coulson, Mack, May, Fitz, and Mace.

Agents of Hydra

While Ghost Rider and the LMDs are big parts of the Marvel Comics universe, the final arc of Agents of SHIELD's fourth season is an inspired original concept. Still, it certainly has roots in Marvel's long tradition of asking 'what if...?' While Simmons wakes up inside The Framework by crawling out of her own grave, Daisy arrives in her apartment where she lives with Grant Ward. Even more shocking, but they're both Agents of Hydra in a world where Captain America failed to stop their overthrow of SHIELD. May is with them as well, while Fitz is essentially the second-in-command and a brutal scientist and torturer. AIDA, meanwhile, has remade herself as Madame Hydra, the ruler of the world and Fitz's lover.

We soon learn that Ward is actually a spy for the resistance, led by Mace and fighting the oppression of the Inhumans and just about everyone else under Hydra. Coulson, meanwhile, is simply a school teacher, though one pushing propaganda for the state. Daisy is eventually able to wake him and May up and bring them into the resistance where it turns out Tripp is still alive and fighting. After some time, they also bring Mack aboard, who's been living a simple life with his daughter who is still alive.

The entire arc is a lot of fun in how it plays with reality and the past of Agents of SHIELD, but it also lets the actors all stretch into new territory. In the end, everyone is able to use a gateway to jump back to reality, but their memories of their lives inside remain. Most of those threads will get picked up in season 5, along with the rest of the fallout from season 4.

Once out of The Framework, the agents have to fight an AIDA who's given herself a variety of Inhuman powers. There's also a slew of LMDs based off of the Russian mercenary dubbed the Superior who was working with the Watchdogs, Radcliffe, and AIDA throughout season 4. Luckily, Robbie returns from his prison and helps the team stop AIDA by granting Coulson the Spirit of Vengeance. Robbie departs using a portal pulled straight from Doctor Strange and the question of what deal Coulson made is left hanging. It's also clear that at least one of the Superior LMDs will return.

With all the main threats handled, the agents decide to head off to a diner to enjoy a moment of reprieve. That's quickly interrupted, however, when time stops and a group of mysterious people arrive behind the agents. The next thing they or the audience knows, Coulson wakes up floating in space, setting up season 5 of Agents of SHIELD.

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