Here's the surprises I don't want my players to be forced to find out prematurely.  Most discussion should be kept to the original thread (link shortly), except where it bears directly on these secrets.

Trim and Noah – That last card?  It's the last card from Trim's hand, and if it's the jack of hearts, Trim wins with a straight flush; if it's not, he doesn't.  Trim sealed it into an envelope and gave it to Noah.  An envelope marked "Hermes."  Then he left, not to be seen again anytime soon.  Noah is not yet sharing this with the others.

Xerae – Thea's actual character's name is Kalypso.  She's a Mercury-born child of Martian expat parents; they got lost in Mercury City, she made her way into the underworld running guns, made her name in the black market interworld.  When she heard about this trip, she decided to make it her jump for the big time, and slipped the real Xerae a mickey, taking her papers and her place.  Having not secured enough points to kill Xerae off in that conflict, she slipped her onto a slowboat bound for the Ninth Gate, to slow down the inevitable pursuit.

Rue – Rue is the great-great-granddaughter of Medusa.  She's a gorgon, and she and her family are among the most elite troops/servants of the Titans.  She's always been a bit of a black sheep, acting more "human" than many of her sisters.  She is, in fact, a veteran of all of the actions which the real Xerae claims – but on the other side.  However, as game opens, her great-great-grandaunt Stheno has just seized control of the family by force, very possibly killed great-great-grandaunt Euryale, subverted an unknown number of the younger brood and probably killed the rest.  Rue has managed to escape and spent her own first session (one-on-one) dealing with the sister delegated to hunt her down and bring her back.  She's now headed offworld shapechanged to look human, blindfolded to imply blindness (or oracular skill, it occurs to me – have to save that thought).  Star's really getting into some of the nonhuman aspect – for example, establishing that normally her hair sees all directions, so she's never snuck up on, she's planning to be surprised by someone walking up behind her and react rather more strongly than we expect for the offense.

Looks from further one-on-one stuff like she may end up headed offworld with Remus, Romulus' brother, on a different ship.  Depends on how much one-on-one it looks like we'll be able to get in, before second session (where I want to get her onto the Argos II so they can all interact, even if they split up later).

Thematically, Rue (and, for that matter but to a lesser extent, Romulus/Remus) raise an interesting point for Nine Worlds in its current incarnation.  The metaphysics of Archons have drifted so far from the Mage:theAscension-esque "illumination" as a core theme that I feel quite comfortable generalizing it and downplaying "Archon" as a distinct type.  An archon is a human with unusual potential, for whom it's interesting to us to see them forced to choose between conformity and defiance.  But near-humans such as Romulus and Rue, while not technically human and thus not technically "archons", can certainly face the same choices – with some interesting variants, such as a certain amount of conformity to the Titan mold of reality for Rue's Arete behaviour – and compel our interest in the same ways.  This isn't even really a point of contention, but it does point out how little of that M:tA remains in the game in its current incarnation.

Gaeolcus ... or rather, J'Iolcus... is the original Jason.  This whole trip is first and foremost his doing.  I'm leaving the details to grow out of play, but it has nothing to do with the fleece itself.  He's using that, and his obvious connection to it, to lead some of the Olympians – starting with Hermes "Trim"agestus – down a berry trail, to some revelation of Zeus' plans.  Nothing more concrete has been pinned down yet, but that's the big collective Bang I'm polishing up for down the road.  What do you do when you've been unwittingly party to a plan to tweak Zeus' nose?

Cross-linkination bootstrapping: the primary thread is here.