The Beginning is a four map campaign for Alien Swarm by Kenny_WWE. This is a version with a fixed download link, included AIN files. Fully compatible with the original VPK, what means that you can connect to each other or to dedicated servers with no problems.
Go to the top of the building to be rescued.
Download
http://gamebanana.com/maps/190160
http://www.moddb.com/games/alien-swarm/addons/the-beginning1
Installation Instructions