Treyarch confirmed that the Zombies mode would return for Black Ops II with new game modes. This is the third Call of Duty game to feature a Zombies mode, following Call of Duty: World at War and Call of Duty: Black Ops, and the first to have game modes other than the traditional Survival mode. Treyarch also confirmed that Zombies would run on the game's multiplayer engine, allowing for a deeper community experience, along with new features. A new, 8 player co-op game called \"Grief\" is also supported, featuring 2 teams of 4 players competing to survive, unlike the previous games which only supported 4 player online co-op. As with the previous installments, each Zombies map contains \"Easter eggs\" side quests, which is used to progress the story. Another new mode, \"Turned\", is introduced with several downloadable content maps, in which one player attempts to survive three player-controlled zombies who must turn the other player into a zombie.
The game is set in the Cold War era. Much of the Call of Duty: Black Ops campaign is told through the eyes of SOG and CIA operative Alex Mason, primarily through flashbacks. Mason awakens strapped to a chair in a room filled with monitors, bombarded with questions by two unknown interrogators about a numbers broadcast. Mason then recalls several events from the past in an attempt to answer their questions, setting up the missions of the game.
Hudson reveals that Dragovich has sleeper cells placed all over the United States, which, when ordered by the numbers broadcast, will unleash Nova 6 in every state capital in the country. As a result, the United States is now at DEFCON 2 and preparing a pre-emptive nuclear strike on the Soviet Union. Hudson further explains that the CIA needed Steiner alive to decipher the numbers broadcasts for them so they could abort the Nova 6 release, but with his death, Mason in the only person left who has any knowledge regarding the numbers station and its location. As the reprogramming of Mason's brain is finally broken, Mason recalls the origin of the numbers broadcast, a ship off the shore of Cuba called the Rusalka. A CIA raid on Rusalka begins, with Mason and Hudson infiltrating the underwater base protecting the ship, and Hudson calling the United States Navy to destroy the Rusalka. In the lower levels of the facility, Hudson and Mason confront Dragovich, and Mason strangles and drowns him to death before escaping with Hudson. He then regroups with Weaver, who declares victory.
If the player decodes the phonetic alphabet code names (X-ray, Sierra etc.) into their first letters, and changing the serial numbers into letters (A-1, B-2) in the beginning of each level, and removing all the Xs, the player will get this message, \"Reznov is dead, or is he dead, there was no body, is he who he says he is\". 153554b96e