Agents of S.H.I.E.L.D. season 5 has come to a triumphant close, and the S.H.I.E.L.D. team has successfully changed the timeline. It seems time isn't fixed after all; it is, as Jemma Simmons notes, an ever-changing, beautiful thing.
Season 5 has seen Agents of S.H.I.E.L.D. transform into a science-fiction series, with the agents attempting to avert a dystopian future timeline in which the Earth had been shattered like an eggshell. Every step along the journey seemed preordained, and that apocalyptic future seemed to be set in place. Ultimately, though, they proved successful - albeit at a price.
That means Marvel Television has embraced what's known as the "Multiverse" model of time - the idea that there are key decision points that act as a fork in the road, creating entirely new timelines in which anything can happen. Curiously enough, though, "The End" seems to see two points of divergence.
The Centipede Serum
At the beginning of the season finale, time was running on track towards the Earth's destruction. Graviton found his way to the Gravitonium, and landed in Chicago, not caring about the fear and terror he was causing. Mack was placed in charge of S.H.I.E.L.D., and he ordered S.H.I.E.L.D. to focus on an evacuation - just as had been expected. Coulson stayed on the Quinjet, refusing to confront Talbot, instead sending Daisy out there. The scene where she shouts back into the Quinjet is a deliberate recreation of the CCTV footage seen in the first half-season.
But there was indeed a difference, and it was one that was - at first - unseen. Rather than take the Centipede Serum, Coulson slipped it into Quake's gauntlet. He believed she could defeat Talbot, but he suspected she'd need a power-up. That decision caused Robin to realize that something was different, the loop had been broken. Because, at the crucial moment before she was about to be absorbed by the unstable Talbot, Daisy injected herself with the Centipede Serum. The power-boost was all Quake needed to send the insane General into space.
The Fate of Fitz
But there's another key difference between the timelines, too. May and Fitz realized that Mack and Polly both died as part of the time loop, and chose to go on board the ruined Confederacy vessel in order to rescue them. They paid a terrible price for this heroism, with Fitz dying in Mack's place. The emotional goodbye scene was poignant and powerful, as Mack said farewell to the man whose sacrifice had saved him.
While this worked in dramatic terms, it was a rather more surprising twist. In most science-fiction stories involving time loops, the point of divergence is a single decision, with all the changes flowing from it. This had nothing to do with the Centipede Serum. It's possible the loop was broken in two places at once; that Coulson broke it, and so did May and Fitz. Another possibility, though, is that Coulson's choice completely broke the loop - and thus, from the moment he slipped the Centipede Serum into Daisy's gauntlet, every single member of the S.H.I.E.L.D. team regained the freedom to choose. In that scenario, Coulson's decision - one that we didn't even see on the screen - opened up the chance for anything to happen.
Questions of temporal mechanics are always tricky in a science-fiction series, and Agents of S.H.I.E.L.D. has handled them well. The season finale does indeed leave some tantalizing questions unanswered as to the nature of time in the Marvel Cinematic Universe, but all that matters is one thing; time has successfully been changed.
Agents of S.H.I.E.L.D. will return in summer 2019.