Imagine you live on a planet that was the last in a string to be colonized by Earth. You have near light speed travel but no real communications between yourself and the other colonies. Your Planetary / Colony government decides to launch a kind of cultural exchange program. You will set out on the ten year voyage to the next closet planet and leave some people, pick up some people and then head to the next planet.
The Problem is that despite your best efforts when you leave the planet you leave something behind. A disease that wipes out most of the population. They have no way to contact you, and no way to warn the planet you are going to next.
By the time you get to the four planet someone or something has figured out a way to get there ahead of you to warn the colony on the planet. There are people on the planet that believe you are a the first stage of conquering force, those that believe you are just a victim of circumstances, and some that believe you are some kind of eco-terrorist.
This prompt was part of a Galley Table Pirate Take over a year or so ago. Want to hear what the cast members came up with? Check it out here.