The zombie-plague phenomenon from the Campaign guide? 
I'm thinking patron/possible job opportunity invites them to a certain world. A few blocks away from the spacesport on a rooftop patio, they're enjoying a nice espresso/cappuccino. <Insert dramatic sequence here> as they notice the upheavel at the space port... followed by a couple of frantic people running as fast as they can blabbering about what is happening. Add in frenzied phone-calls and then the appearence of some zombies..
I'm thinking at that point, with 1 spaceport in the world the adventure breaks down as follows:
a) Find shelter and survive initial onslaught.
b) Determine opportunities for unscrupulous gains (10 tons of illegal weapons? hmm) - adhoc
c) Develop and implement the plan to make it back to the space-port and leave the planet which is now a red-zone.

I'm thinking patron/possible job opportunity invites them to a certain world. A few blocks away from the spacesport on a rooftop patio, they're enjoying a nice espresso/cappuccino. <Insert dramatic sequence here> as they notice the upheavel at the space port... followed by a couple of frantic people running as fast as they can blabbering about what is happening. Add in frenzied phone-calls and then the appearence of some zombies..
I'm thinking at that point, with 1 spaceport in the world the adventure breaks down as follows:
a) Find shelter and survive initial onslaught.
b) Determine opportunities for unscrupulous gains (10 tons of illegal weapons? hmm) - adhoc
c) Develop and implement the plan to make it back to the space-port and leave the planet which is now a red-zone.