From the introduction:
The characters begin on their way to a week long camping trip—one final trip with the boys before Steven gets too sick to do this anymore. Between a pretty powerful storm that sweeps through the area, rock climbing, and spelunking, the characters will have an opportunity to develop their relationships and get used to the game mechanics. On the way home, they begin to see that things are strange. No one is on the highway and, when they stop at small towns along the way to gas up, they find that everything is locked up and everyone is gone. Closer to home, they find massive pileups, burnt up cars and corpses, and - finally - their first zombie.
Once in town, each character has people they care about in town that need rescued. The lynch pin, Nancy, is with a group who ended up in the college radio station. If the group can reach a radio, they'll find the station and her voice calling for help.