Left 4 Dead 2 has a new add-on campaign, and it's called "The Sacrifice". This DLC for the Xbox 360 is a prequel to "The Passing", which features a meeting with three of the survivors from the original Left 4 Dead video game, where they learn that Bill, the fourth original survivor, sacrificed himself for his fellow comrades.
In this new prequel, the plot revolves around the meeting of the two groups of survivors in "The Passing", from the vantage point of the Left 4 Dead characters. Except now, you can choose who is sacrificed, besides Bill, for your choice of Bill, Zoey, Francis or Louis.
This video series will walkthrough the gameplay of the new download, showing Zoey taking the fatal sacrifice against the zombies.