[This is a review of the Agents of S.H.I.E.L.D. season 4 finale. There will be SPOILERS.]

As many fans are well aware, Agents of S.H.I.E.L.D. season 4 has been split up into three distinct storylines. The first introduced Robbie Reyes aka Ghost Rider (Gabriel Luna) to the Marvel Cinematic Universe as well as the Darkhold and the magic that comes along with it. After Ghost Rider disappeared to a different dimension with his uncle Eli Morrow, Agents of S.H.I.E.L.D. shifted focus to Dr. Holden Radcliffe's Life-Model Decoys, particularly Aida, who had read the Darkhold. Most recently, Agents of S.H.I.E.L.D. dove into the Framework, a simulated reality created by Aida with some changes to history that established a world in which Hydra ruled and S.H.I.E.L.D. had been defeated.

However, when the agents learned of Aida's true endgame -- to create a human body for herself in the real world, thus granting her free will outside of Radcliffe's programming - they exited the Framework and returned to reality in order to defeat Aida. Not all the agents exited the virtual reality though, since Mack stayed behind in the Framework. Last week's penultimate episode of Agents of S.H.I.E.L.D. season 4, 'The Return', set the stage for this week's finale, with Ghost Rider returning from whatever dimension he had been in and Yo-Yo heading into the Framework in order to bring Mack back.

In Agents of S.H.I.E.L.D.'s season 4 finale, 'World's End' -- written by Jeffrey Bell and directed by Billy Gierhart -- Coulson and the team reunite with Ghost Rider, asking for Robbie's help in defeating Aida. Then, the agents race to thwart Aida's plan to end the world as they know it.

Ghost Rider is Back & Better Than Ever

Agents of SHIELD Season 4 Finale Ghost Rider

Since both Ghost Rider and Aida's new human form are connected to the Darkhold, it only makes sense that Robbie's sudden return from the dark dimension right after Aida becomes human isn't a coincidence. As a matter of fact, because the Spirit of Vengeance and the Darkhold are from the same darkness, and since human Aida was created through the Darkhold, he's the only thing that can defeat her. This particular revelation works to bring together the major aspects of this season's three storylines - with the Darkhold as the unifying thread.

But, defeating Aida isn't as simple as one fight with Ghost Rider since the LMD-turned-human has a number of Inhuman powers at her disposal. Fitz explains to Simmons early in 'World's End' that he was able to give her Inhuman abilities by extracting DNA from his test subjects. He mentions Gordon (the season 2 Inhuman tied to Afterlife), Lincoln Campbell, and Vijay Nadeer. Additionally, Aida learns quickly to avoid Ghost Rider after he injures her arm with his fiery chain and it doesn't heal. So, Coulson comes up with a plan to trick and defeat her.

One of Agents of S.H.I.E.L.D.'s strengths is in structuring its storyline to maximize shock value and the show epitomizes this particular tactic best in 'World's End'. Rather than explain ahead of time how exactly Aida plans to end the world or how S.H.I.E.L.D. plans to defeat her, the episode jumps right into the action. Daisy breaks into the S.H.I.E.L.D. inquiry and shoots Talbot in the head, with the show only revealing afterward that it was an LMD; Aida tortures and kills Simmons in front of Fitz, only for that Simmons to be revealed as an LMD; Coulson lures Aida to him, only after revealing he's made a deal with the Rider for its help in killing her - and that was Coulson's plan all along. Of course, Agents of S.H.I.E.L.D. runs the risk of overusing this particular tactic, but it makes for such an exciting hour of television that it's forgivable.

As for Ghost Rider's part in 'World's End', the special effects team on Agents of S.H.I.E.L.D. pulled out all the stops, creating plenty of fiery transitions of Robbie - and, in one case, Coulson - to the Rider. Additionally, there are a number of beautiful and, frankly, cool shots of Ghost Rider, the one of which is a slow motion sequence when Robbie confronts Aida on his own and slashes his chain at her, but she teleports away. This and other exciting shots like it help to elevate 'World's End' even beyond what fans might expect from a season finale episode.

Not With A Bang...

While Coulson's team has plenty going on in terms of finding a way to defeat Aida, there's also a ticking clock on Yo-Yo's mission inside the Framework since the virtual world is in the process of being deleted. Last week's episode left viewers with the cliffhanger of Yo-Yo waking up in the Framework strapped to what appears to be an experimenting table within Hydra. This week picks up with her being rescued by Radcliffe, who takes her to Mack. Yo-Yo struggles to figure out how to convince Mack to leave Hope and return to the real world, which is made more difficult as the Framework disappears around them.

Mack's storyline throughout season 4, which introduced Hope earlier on, has become an emotional grounding point for the show and it works in much the same way in the season finale. Though Yo-Yo's attachment to Mack isn't as well developed, his love for his daughter has proven to be the most heartbreaking aspect of the Framework storyline. That particular arc comes to a head when Mack is holding Hope close and refusing to let go, only for her to disappear from his arms. It's an incredibly emotional moment, one that lingers as fans are left wondering what this means for Yo-Yo and Mack - and whether they'll decide to exit the Framework after all. 'World's End' doesn't leave fans wondering too long though as both of them wake up.

Radcliffe, however, is left in the Framework with no body to return to since Aida killed him earlier this season. With everyone he cares about gone or blinking out of existence, he takes a bottle of alcohol to watch the sunset on a beach, monologuing to himself on the meaning of immortality without Agnes. In another beautiful shot that should earn Gierhart plenty of recognition for his work on 'World's End', Radcliffe begins quoting T.S. Eliot's "The Hollow Men." However, he blinks out of existence, his drink falling into the sand, before finishing the famous quote: "This is the way the world ends / Not with a bang but a whimper." It's a beautiful end for not only John Hannah's character on Agents of S.H.I.E.L.D., but the entire bittersweet Framework arc - which brought back fan favorites who are now gone again from the series.

Agents of S.H.I.E.L.D. - In Space!

With Aida defeated, the Framework gone, and Ghost Rider traveling to a different dimension with the Darkhold, that leaves Coulson's team dealing with what's left of S.H.I.E.L.D. and their once again ruined reputation. The group heads to a diner for a meal together when they're confronted by mysterious and seemingly government-affiliated agents. However, things take a turn for the weird when the lead agent uses a device to freeze Coulson and his team before saying, "The window closes in less than two minutes. Take them." Next we see, Coulson wakes up in a room and opens a window to look out on what appears to be an asteroid belt, presumably from aboard a spaceship.

The whole sequence plays out like a surrealist sci-fi setup that appears to take the series in an entirely different direction. Season 4 had delved into magic and mysticism with the introduction of Ghost Rider and the Darkhold, even taking a sci-fi concept in the LMDs and giving them a more fantasy arc. However, with Ghost Rider, Aida, and the Darkhold gone, Agents of S.H.I.E.L.D. seems to be returning to its sci-fi roots by heading into space. Of course, what exactly these final scenes mean for the future of the series remains to be seen, but they certainly set the stage for a different and exciting Agents of S.H.I.E.L.D. season 5.

Next: Agents of S.H.I.E.L.D. Season 5 Debuts Midseason

Agents of S.H.I.E.L.D. will return for season 5 on ABC.