The Observers: The Human Division, Episode 9

In an effort to improve relations with the Earth, the Colonial Union has invited a contingent of diplomats from that planet to observe Ambassador Abumwe negotiate a trade deal with an alien species. Then something very bad happens to one of the Earthings, and with that, the relationship between humanity's two factions is on the cusp of disruption once more. It's a race to find out what really happened, and who is to blame.

"The Observers" is a tale from John Scalzi's The Human Division, a series of self-contained but interrelated short stories set in the Old Man's War universe.