Not content with unleashing a full-blown zombie apocalypse, Valve has come up with the second most socially awkward event imaginable: inviting characters from the original Left 4 Dead to hang out in the sequel's first DLC campaign. Bill, Louis, Zoey and Francis will meet with the stars of Left 4 Dead 2 in "The Passing," which Valve VP of marketing Doug Lombardi calls "the most important campaign in the Left 4 Dead story, as all the Survivors are being called together in one campaign." It's targeted for release in early 2010 on Xbox 360 and PC.

In addition to a co-op campaign (set in rural Georgia) and a new "co-operative challenge mode of play," The Passing will offer new content for Survival, Versus and Scavenge modes. Playing as the L4D2 cast, you can also expect to encounter a new melee weapon, firearm and "uncommon common" zombie.

We can't wait to meet up with last year's survivors again ... oh, assuming they really are still survivors.

This article was originally published on Joystiq.

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