North America is balkanized, split into twelve smaller countries, most of which call themselves the United States of America (except for two which call themselves Canada and one Quebec). Teleporting aliens (the Dandelions) have discovered Earth, which means that the other races of the interstellar Confederation have found us.
All trade agreements are tentative and depend upon Earth's acceptance into the Confederation. We are engaging in an exchange of art objects (yeah, I know I stole this from _Doorways In The Sand_), and Earth seems to have lost one of the alien artifacts. [When I ran this, it was a "pure" AI they lost; a wirehead had accidentally jacked it into the world network. Choice of artifact depends upon how the artifact was lost (by accident or not) and who is after it.]
Each country wants to be the one to find it. [Country of choice], which had the artifact when it disappeared, doesn't want the news to get out, though all the security services know about it. A subgroup of carnivorous aliens don't want the humans to find it.
Alien motivation: Humans may make amusing game or food animals, but it's not practical to ship them across interstellar space. However, if humans fail to make it into the Confederation, the aliens can bid on copyright to human DNA, producing clones for whatever purposes they want. [Intelligent species own their own copyrights.] Aliens may also have internecine struggles.
The characters could be innocent bystanders, diplomats, detectives, police officers, spies for the L-5 colonies, ninjas, yakuza...