1. I need to have some filler to get the ball to last for an entire session. Some events that can happen that are not related to the assassination attempt. If these events can lead on to further adventures, that's a plus.
Ever read a trashy romance novel?
They are full of all kinds of great, generally non-physical (i.e., no fighting) problems that can crop up in such situations. Keep in mind that "It's
THE social event of the month. All the impressive hoity-toitys will be there." So, with that in mind, here's a couple thoughts:
1. It's Just Like High School ... : Let your players pick up on the fact that there are two (and likely more!) loose groupings of people. Let someone with a high Spot check (or Wisdom ability) notice the groupings, as well as a couple key members (the suns about which the planets orbit). Now, lacking appropriate Knowledge skills, they probably won't know who these people are off the top of their head; they'll have to ask around. This might be a good way to introduce certain highly influential players (future patrons, perhaps?).
2. Bob Doesn't Like Suzy, Who's Fighting with Jane ... : It's obvious, given the above, that at least two of the groups don't like each other - there's really no intermingling. Let players notice the one or two people who seem to be acting as go-betweens between the two factions.
3. Pull a Cinderella: There's someone at the ball who isn't really supposed to be. Her manners (or his!) don't seem to fit - rather like your PCs don't really seem to fit. Perhaps she's an adventurer as well, hidden in the crowd as a body guard (or assassin?), or perhaps she's a scullery maid who's been given a chance to mingle, for one glorious evening, with the social elite.
4. Pull a James Bond: While patrolling the floor, one of your PCs suddenly finds himself (or herself) surrounded by a gaggle of elder women or men, and one of the appropriate age and gender. He or she pulls the PC onto the dance floor with the aid of the elders, and forces him to dance a complicated court dance. Using the rules from the Complete Adventurer, the NPC is taking a rather large penalty on his / her Perform (Dance) check in order to give the PC a sizeable bonus, if required. If they dance well enough - taking a few moments in which you can change focus to another PC - the crowd applauds and the gracious NPC presents the PC with a token of his / her esteem. Perhaps it's a pin, perhaps an ornamental dagger, perhaps it's just a scarf, whatever. If the PC dances poorly, he's politely chuckled at, and the NPC apologizes profusely, offering a token (see above) by way of apology.
The token is useful - magical, well-made, etc.; expensive - jeweled, finely wrought, etc.; or dangerous - it's a tracking device, it'll implicate the PC in the assassination attempt, etc. Your choice.
5. Crash the Party: Have the Sharn equivalent of Greenpeace or PETA show up. The come in through a window that was [carelessly?] left unlocked, or by infiltrating the waitstaff, or whatever fits. They are protesting for or against Warforged rights, the exploitation of the goblinoid underclasses, remaining Karrnathi undead forces in the vicinity of Audair, whatever is appropriate. Perhaps they throw blood on people. Have a short scuffle in which the PCs may or may not be asked to participate, before they are escorted out.
6. Romeo Must Die: Magic happens, a shot rings out, whatever, but someone is dead and his / her lover is standing over the body. Is this a simple, clear-cut case of a woman scorned? Was it the work of someone else, an attempt at framing the poor survivor? And, hey, who's watching the ambassador's daughter during all the commotion?
EDIT:
BG's got some great ideas as well!
