Possibility: Conflicting orders: Most of the Jaegers we've seen seem to be going with "we serve Wulfenbach to better keep an eye out for any remaining Heterodynes"; we don't know if this is the initiative of the generals, or was due to some sort of final orders. If there were some other (previously-isolated) group of Jaegers with some other final mandate from Barry or Bill, there could be...disagreements. Justin: Very neat idea! I like the notion that there's some sort of Heterodyne legacy in the background of the game, so this has real potential.
Possbility: Conflicting loyalties: A Spark has discovered some way to suborn Jaeger loyalties, and now has some of his own. Or a Spark is aware of the Wulfenbach-Heterodyne dynamic to the Jaeger's loyalties, and is trying to convince them that serving (him/her) would be in their best interest - that Wulfenbach will inevitably turn on Agatha, and that keeping Wulfenbach strong is only going to hurt the Heterodynes at this point. Justin: possible, but this may be too much division, given the three-Agathas plot already lurking in the background as a way to divide the Jagers.
Possbility: Urgent business: There's something vital to Heterodyne interests which needs dealing with, soon (read: first hour or two of game-time) - but they can't ask Agatha, since they don't know which one is her, and revealing the business to an impostor would be bad. There are differing opinions about how this should be dealt with. Justin: not bad: fits in with the overall plot web, and might combine well with the above. Also, has a lot of potential for improv Jager comedy, which I assume many of the players are looking to do.
Putting all this together into current form: initially, we're going with a combination of these ideas. Dimo, Oggie and Maxim have respectively found themselves believing that the real Agatha is Mirror-Agatha, Helen and Maria respectively. Each is reasonably sure that he's right, but not enough so to convince the others. Meanwhile, Jenka has begun to puzzle out what's really going on here: she can sense that they are close to the device that brought them to this world in the first place. There is hope of going home, but only if the true Heterodyne heir releases them from their contract of service. Moreover, no one except the Heterodynes are supposed to know about the nature of the agreement. So they need to be absolutely certain of who they are talking to.
Gil should be written as a counter to this plot, and maybe DuPree as well. (And Von Pinn is deeply torn, standing between races as she does.) Klaus has sensed a certain restlessness among the Jagers of late, and is very concerned ever since Agatha showed up on the scene. The Jagers are utterly essential to the Empire: they were Klaus' first allies in his fight to restore peace, and still make up the backbone of his army. If they were to become enemies, or even simply to decide to sit on the sidelines neutrally, it is entirely possible that the empire would fall apart, and chaos would reign again. This plot truly is zero-sum: there is a real and severe cost to the Jagers going home. Wooster should probably have an explicit objective of weakening the Empire in any subtle ways he can do so, and should be sensitive to this matter: he should probably be encouraging and maybe even explicitly helping Jenka and the Generals to find a way for the Jaegers to get home.
Maybe work Theo into this plot, by getting the Mongfishes into the back story.
Notional revision (Darker)
(As discussed on Diary, to avoid the "remove the Jaegers from the universe" sadness. This is brainstorm and may not be coherent.)
It has been heavily implied in canon that the Jaegers need to serve someone. Perhaps this is not merely a psychological need, but they actually need something - some sort of (treatment / nutrient / Metaphysical Thing / Symbolic Thing / periodic ritual that requires a great deal of effort to enact / small fruit / whatever). Not often, but enough such that without it, the Jaegers will inevitably decline and die off. They serve Wulfenbach to accomodate this need, and because in the present political environment, if they weren't working with him, he'd probably be working to exterminate them.
If the need is physical: one of the reasons Jenka stays in touch with the wild Jaegers is not just to relay information, but to bring them the occasional (whatever-it-is: bug, small fruit, glowing rock...).
If the need can be satisfied in the place from which they came, portal access would be highly useful - but they'd still need Agatha's permission, as deliberately leaving this reality (even temporarily) would violate their oath to the Heterodynes. (Note: This assumes the "Jaegers aren't from here" origin is kept; with this variation on the plot, it's not at all necessary, and it'd actually make more sense if they were constructs - the need would have been deliberately built-in.)
The need might also be satisfyable in some other way - if it's temporally related, via the Brigadoon Effect, for instance. If it requires a Spark to create (whatever-it-is), they could seek out another patron, but that'd probably only be worthwhile if it looked like the political balance was going to radically change (while Wulfenbach would undoubtedly have a harder time without them, he'd still be more potent than any other single power; jumping ship for anything less than Heterodyne loyalties or total independence from Sparks would likely be a bad deal).
Another idea (Justin)
We already know that the Jaegers have a lot of trouble being separated from the tribe for long periods, but what if the instinct is slightly different than merely being together? What if contact is the fundamental instinct? It isn't so much a matter of needing to be together all the time, but rather that they have a core instinct of sending word back to the larger group, of where they are, and how they are doing, and receiving approval for it? Yes, it's a little esoteric, but not really any stranger than the real-world spawning-ground instincts.
That has reasonably nice game effects: it provides powerful motivation for them to get involved with the main plot of the game, but does not have a game goal of leaving the world. They've been on their own for centuries, and there's a certain mental agony to the whole thing: not knowing if they are doing right, or whether their hats meet with social approval. They just need to talk to the homeworld -- that will be enough to get them by for a good while. Perhaps one Jaeger needs to go through, get word, and come back to tell the rest that it is okay. Just to make it a little more interesting, we might posit that it is a great honor to be the one who goes through; they get to decide which one goes.
I don't know if that's sufficient plot for the Jaegers -- we might need something like Darker's idea above as well -- but I like it as a plot for them. We could even tie it into the Ancient Contract, which might have obliged the Heterodynes to do what they could to help the Jaegers maintain regular contact with home. Heck, that might even have been what Mirror-Agatha was working on when she was trying to operate the Mirror of Amagog: it would be in-character for her to know more about what needs to be done than anyone else, and to be trying to honor the family's commitments.
Final concept (Justin)
Okay, I'm tying all this together. Curiously, it all got crystallized by the basic question, "What's with the hats?" It's a bit strange and silly, but hey -- I'm postulating that the Jaegers are essentially aliens, so strange is okay.
The high concept is that Jaegers get their near-immortality from a general shared force that they simply call "Life". Life allows them their powerful regenerative abilities, as well as most of their intelligence. If they have enough Life, they can recover from almost any injury.
They have a specialized organ at the top of their heads, which manifests as small "Lifebumps", where this is stored and transmitted. The size of one's Lifebumps is directly related to how much Life one has. The leader of the Jaegers is known as the Hatless, and has the largest Lifebumps, making him both the strongest, most resilient, and most intelligent of the lot. The rest of the tribe pay homage to him by giving him a small portion of their own Life, which is what gives him the large Lifebumps. At this time, General Khrizhan is the Hatless.
Life is shared via the Lifebumps: when one Jaeger is badly injured, the others nearby instinctively share a bit with him, to help him regenerate. This is part of why they have such an intense tribal instinct: so long as there are many Jaegers in one place, it is very difficult to kill one.
Life is not limitless: it is used up, very slowly, as they need to regenerate. When they are on their homeworld, they naturally regenerate it from the environment. The result is that, over the centuries, the Jaegers are getting weaker and stupider. Hence, the motivation to use the Mirror of Amagog to get someone back to the Jaeger homeworld. The Jaegerkin bluesheet is explicitly written so that they don't all have to go home, or even necessarily want to. But they need someone to get home, and bring back enough Life to regenerate the tribe here.
Note that Life is more or less the same force as the Spark, and they can receive it from Sparks, but it requires altering the Spark's genetics to do so. The Heterodynes did this willingly, binding the Jaegers to them. Klaus isn't willing to share his own Spark -- ultimately, he is a bit too self-centered and monomaniacal to do so -- but he does understand what's going on. This is one of the reasons why he is probing the nature of the Spark: he is trying to live up to his end of the bargain, and figure out how to make other Sparks share a bit of Life with the Jaegers. Gil knows about this, and likes the principle of helping the Jaegers, even if he's just a smidgeon uneasy about the means. Von Pinn also knows about it, and thoroughly disapproves.
Characters In Game: Baroness Dimo DuPree Gil Jenka Maxim Oggie Von Pinn Wooster
All Characters: Baroness Dimo DuPree Gil Jenka Maxim Oggie Von Pinn Wooster