Chris Ashton, co-founder of Turtle Rock Studios, actually posted on the game developer’s forum sites a link to the third-party source where gamers can download the campaign.
Ashton says that it is a gray box work, which means that some features are incomplete but it is playable from beginning to end.
The “Damn It” campaign was never finished. It includes a couple of Survival maps that never came out. Overall, it stitches together the game’s “Dead Air” and “Blood Harvest” campaigns.
Installation instructions are available on the download page provided by Turtle Rock. There are a number of issues acknowledged in the add-on’s notes because it does not include any code changes that could resolve them.
There’s also a very detailed map of the setting and the level design, which function as a nice strategy guide for those exploring “Damn It.”
The campaign begins at an airstrip and moves its way through an apple orchard, into a deep ravine, through a covered bridge and a campground before the big finale at a hydroelectric power dam. It is set up so that players can split up to work independently, instead of cooperatively, to fend off the zombie onslaught and reach the conclusion.