So, I've been wracking my brain for weeks trying to figure out the deal with that man who Lake stole the pod from. I'm in the corner that doesn't see him as a potential protagonist, but i couldn't see any real roles for him besides a companion to the protagonist (and even then, I couldn't figure out how he'd fit in to the plot line as a whole). And then, while browsing YouTube, it hit me.
What does the man not have? A number.
Which characters can safely be assumed to show up again in book 3? The Apex.
And what's the Apex's stance on people with no numbers?
If Grace, Simon, or a raiding party got wind of a passenger with no number, you can bet your Atticus they'd be shocked and confused. And given their misguided belief that One-One is trying to kick the humans off the train, I can see them believing that he somehow found a way to remove the numbers from passengers entirely. Simon would probably try to wheel him, but Grace would most likely disagree with this decision, seeing how he is human.
So you've got a gang of murderous pirate kids with cool grappling hooks going after this old man who doesn't even have any idea where he is or how he got here. While him joining the Apex at Grace's request is a possibility (and i admit it'd make for some pretty interesting plotlines), I think it's more likely that he'll try to flee, ending up right where i want him: With the protagonist. And that brings us to a more interesting question....
So who the curse word is the book 3 protagonist?
Given that all signs point towards the Apex as book 3's main antagonists, and that they appeared in episode 7, the same episode that book 1 used to set up book 2's protagonist, it would make logical sense for the lead character of book 3 to be an Apex member, most likely one who decides to defect in hopes of escaping the train. As the Apex, with the exception of Grace & Simon, is made entirely up of what seems to be kids of Tulip's age or younger, a young protagonist is the most logical.
I've seen a lot of speculation that the girl with the dead lizard who Lake failed to steal a number from would be protagonist, and despite Infinity Train's tendency to introduce major characters for the next book in the book before them, i really doubted it: Her character arc just didn't seem like enough to engage audiences.
But then I looked at the following idea: What if she joined the Apex? What if we had a protagonist join the Apex on screen, and then learn to accept the past and leave them as part of her character arc?
Every Infinity Train protagonist group so far has had 3 members, and i don't expect book 3 to be an exception. There's always a cute animal, as we've seen with Atticus and Alan D, and I think that introducing an animal which the Apex tried to stable or wheel as the protagonist's companion would make sense to show her defecting.
Enough with characters, time for the plot!
I really couldn't think of another way to do this section, so I'm going to be going episode by episode, deciding on what events i think will happen when. This is still rather rough, though.
Episodes 1-2: Dead Lizard Girl (let's call her the protagonist from here on out) boards the train, is confused and scared, encounters the Apex, and decides to join.
Episode 3: After a small time skip, we see the protagonist's life as an Apex member. Her number is higher, but she doesn't care, as she's living the wild life, and believes the two nice grown-ups who're teaching here about the ways of this new land. However, she starts to question them after being a witness to a more brutal raid, but doesn't defect yet.
Episode 4: The old man makes his first appearance, as the protagonist finds him during a raid. She overhears Grace and Simon talking about whether or not to wheel the man, then sees the Apex mistreating the animal companion, and realizes what the Apex are doing. The episode ends with her defecting from the Apex and bringing the old man and animal companion with her.
Episodes 5-7: These are my roughest episode outlines. The protagonist and old man are headed to the tape car (which the old man followed Lake to, but wasn't able to get into), seeking a way to get the old man a number. Meanwhile, it's discovered that the Apex are planning to attempt to reach the tape car to find Amelia, their goddess. I want the cat to appear in here, as well as the book 4 protag, but can't figure out how.
Episode 8: We arrive at the tape car, where Amelia turns out to be, and a pitched battle at the number machine ends with Amelia attempting to show the Apex how wrong their ideology is. Grace realizes her mistake and shows signs of wanting to reform, but Simon isn't having any of this: he either straight-up murders Grace and takes control of the Apex, then heads to take out One-One (a motive for him that should have been established prior), or splits the Apex, taking half of them for the same goal. On the bright side, the old man gets a number.
Episodes 9-10: I have no idea, honestly. I think it should all culminate back at the Engine. if Grace survives, then her half of the Apex could act as an ally to the protagonist, via the "enemy of my enemy" philosophy. Obviously, both the protagonist and the old man get off the train, and Grace and/or Simon are left trying to get their number down (if either survives).