Warning: many spoilers ahead for Episode 4 of Agents of S.H.I.E.L.D. Season 5, called "A Life Earned."
When Season 5 of Agents of S.H.I.E.L.D. debuted back in the beginning of December, there was one noticeable absence among the group of folks transported through time and space to the Kree-controlled Lighthouse. Good old Leopold Fitz was nowhere to be seen, left behind on Earth while all his friends and lady love were sent very far away from him, because nothing good ever happens to Fitz. Aside from a cryptic message in the Season 5 premiere that Fitz was "working on it," he simply hasn't been around. Now, S.H.I.E.L.D. brought Fitz back in a big way, but not how we expected.
Fitz didn't turn up in "A Life Earned" until the very end, but it was a heck of an entrance. He appeared as part of a crowd of buyers who had visited Kasius on the Lighthouse with the purpose of buying Inhumans. Having captured Daisy at the end of last week's episode, Kasius knew that he was going to be a very rich man once the bidding was over, and he proposed an exhibition of Inhumans to show off their abilities. One potential buyer wasn't happy with this and emerged from the crowd, wearing a mask to obscure his features. He protested that since Daisy is the Destroyer of Worlds, she should have to fight to the death. Daisy was shocked when he unmasked himself, revealing that he is none other than her pal Fitz.
Now, unless you detected that hint of Scottish accent in Fitz's voice before he unmasked himself (or if you noticed that the buyer's outfit matched what Fitz was wearing in all the S.H.I.E.L.D. Season 5 promo pictures), the twist probably came as quite a shock. After all, as far as we knew, Fitz was "working on" the problem back on Earth in 2017, using his intellect and engineering wizardry to figure out how to bring his friends back. If the guy could work out a way to fetch Simmons from Maveth, surely it was only a matter of time before he staged a grand rescue.
Instead, Fitz emerged from a pack of pretty dastardly characters who were all present to watch Inhumans fight each other for sport. His first move was to demand that Daisy be put in even more danger than she would have been, and unmasking himself in front of her was a very risky move. If she had reacted to his sudden appearance, she might have accidentally given the game away. We can only hope that Fitz has a long game in mind here. At least his plans seems to have more finesse than when he tied a rope around his waist and jumped through a hole in the universe.
Given that Season 5 so far has taken place 90 or so years in the future from where Season 4 ended, we should probably consider the possibility that this wasn't Fitz at all, but rather a relative of Fitz who just so happened to look like Iain De Caestecker. S.H.I.E.L.D. wouldn't be the first show to try to pull something like this off, and it would make for a crazy twist. Still, the man in the mask spoke with a very Scottish accent, and accents logically would have faded away in the time since Earth was destroyed and the remnants of humanity were consolidated into the Lighthouse. My money is 100% on Fitz being the one who turned up in "A Life Earned."
Assuming Fitz isn't suddenly a bad guy embracing his former Framework self, the odds are that he has some big ideas on how to rescue his friends. In fact, he may be the variable that turns the tide in their favor, especially since May seems to be out of the game after her showdown with Sinara. Fitz presumably has information at his disposal, and there's no denying that he's very intelligent. Coulson and Co. have really been crippled by the absence of a scientist ever since Simmons was taken by Kasius; Fitz's reappearance could make a huge difference. In fact, given his history with gadgetry, he may be able to figure out how to get the deafening contraption out of Simmons' ear and deactivate the devices controlling the Inhumans' powers.
Since the episode revealed that Kasius intends to destroy the Lighthouse and all its inhabitants once he has the profits from selling Daisy, time really is of the essence. There's also the point that we now know that the Kree have been using Inhuman DNA to breed humans (and have been controlling the fertility of the human population), which basically means that they need to be taken out ASAP. Of course, it's possible that Fitz did the Season 5 equivalent of tying a rope around his waist and jumping through a hole in the universe and is totally winging it in the Lighthouse. We'll have to wait and see.