Continuing its tradition of updating games with free downloadable content (free for PC that is, it'll be 560 MS points on the Xbox 360), Valve has announced that it is plans to release the next Left 4 Dead DLC on October 5. Called "The Sacrifice," the pending expansion is a prequel to "The Passing" L4D2 DLC, which landed back in spring.

The new campaign will be available for both L4D and L4D2 and takes placed from the original Survivors' perspective as they make their way South. Borrowing a tactic that's used in nearly every zombie flick, Valve says players will have to sacrifice a comrade to complete the finale (think back to Bill's absence in The Passing).

Along with the trailer embedded above, Valve has released the first three installments of a four-part comic. The initial entries available online here (including downloadable PDF copies), while the fourth is set to arrive next Tuesday with The Sacrifice.