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.
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.