Undead Nightmare is a modified expansion of the 2010 video game Red Dead Redemption,[1] an open world Western action-adventure in which the former outlaw John Marston is coerced by the federal government to capture former members of his gang in exchange for his family's freedom.[2] Undead Nightmare is an alternate timeline expansion that adds a new full-length story in a zombie horror theme and reworks the base game's environment to appear dark and spooky. As corpses begin to rise from the dead to become flesh-eating zombies, some of the living go into hiding and others become hostile.[1] John seeks to find the plague's cause and its cure for his infected wife, Abigail, and their infected son, Jack.[3] The game's story lasts about six hours and includes new cutscenes, voice acting, and music. It is accessed separately from the main game menu with its own save files.[1] It does not share play progress and items from the main game,[4] nor does it require the base game in any form