 To connect the events in "The Passing" to that in "Left 4 Dead", Valve released another add-on in October 2010 for both "Left 4 Dead" and its sequel, entitled "The Sacrifice"; the events of the add-on take place before "The Passing" and tells how the "Left 4 Dead" survivors come to encounter the group from "Left 4 Dead 2", and how one sacrificed themselves for the safety of the others.Valve announced a 190-page digital comic that has been revealed in four parts in the weeks leading up to the release of "The Sacrifice".Part one was released on September 14, 2010, with a new part scheduled for release each week until "The Sacrifice"'s October 5 release.