Jim's smile his bright, maybe a little mischievous, but mostly excited. He takes her hand and leads her through the party, not caring whether they get any looks. They don't, really, people just generally don't care that much, and besides everyone seems to have their focus elsewhere.

Of course that while they're still at the party, Jim feels clear-headed and absolutely at ease about all this. Reality coming down on him when they step outside will be another thing entirely...