In his interdimensional travels, Amagog came across a world that was essentially his world, 200 years advanced. He left behind some Nostradamus-style cryptic descriptions of what he found there, in his diaries. One of those appears to concern the situation of one or more of the players. This should drive them towards the Castle, and give them an idea of what to do.
Note that Amagog did not actually travel into the future -- it was still a parallel universe. And the prophecy itself has potentially affected the outcome. So we should feel free to specify what the outcome is, but not have that dictate what really happens: it's merely a possible outcome. This should be written in florid prose, and should be just a bit obscure, but clear enough to make reasonable guesses as to who is who.
This should all tie together with the Legacy plot. One of Sarah's specific goals is to prevent this slightly bleak future from happening. It is explicitly up to her to decide which bits of this are good and which are bad.
Let's take the prophecy idea, and have it play into a lot of different plots. Say that the prophecy is set about a year in the future, and shows one possible outcome, taking a number of the plots into account. It's essentially salt, added to spice those plots up and give them more oomph and conflict. Some components:
Of course, the interesting question is who has the prophecy itself, and how widely it is known. This screams out to be Moloch's principal plot.
Let's play it this way. This was specifically set up by Amagog, who knew (we may just handwave how) that the crucial time would be when his last descendant met his greatest achievement. The prophecy is essentially programmed into Moloch's DNA. As of the background, he has begun to feel strange, for the past couple of days. At some point when he and Sarah are in more or less the same place, he finds himself thrown into a strange trance, and speaks the full prophecy directly to her, in full public view for anyone who is present to hear -- ideally, we should time this sometime when they are both relatively in public, and it shouldn't be clear to whom it is addressed. The Prophecy is addressed directly, if vaguely, to Sarah, but should probably be worded so as not to give the show away -- address it as "child of my thoughts", or something like that.
Note that the Prophecy does not exist in written form, it's in Moloch's head. The act of giving it is mentally costly to him. It costs him one point immediately when we force him to read the whole thing, and there is (say) a 1-in-3 chance of it costing him another every time he looks at the sheet giving it. Thus, a number of players have motivation to hear it again, but he should be written to demand something from them to give it: this is scary stuff. If they think to ask her, Marie should be able to brew up a fortifying potion that will restore up to, say, two points to him from this.
For her part, Sarah should be vaguely expecting this. Before he went away, Amagog told her that he has left her the responsibility for executing his legacy, and he will tell her the details when the time comes. Beyond that, she doesn't know what to expect.
The actual Prophecy itself can be found in Prophecy Text, and is given to Moloch ten minutes after he opens his [Distortion Sensitivity]? envelope for Sarah.
Characters In Game: Moloch Sarah
All Characters: Amagog Moloch Sarah
To Do:
Write the fully-detailed Prophecy, and put it into Moloch's contingency envelopes. Ideally, write it in sonnet form. Make sure that it is obscure enough that only the targets of each line, and those immediately around them, are likely to guess at their import.