Details have just surfaced for the fourth map pack for Call of Duty: Black Ops, titled Retaliation. While Treyarch has only recently began development on the map pack, we still have quite a bit of information on it. There will be four multiplayer maps included in the map pack, titled Mansion, Cargo, Metro, and Harbor. Mansion takes place in Castro's secret compound in Cuba. Cargo takes place in an frozen shipping center in Greenland. Metro takes place in an urban city in Vietnam. Harbor takes place in an abandoned shipyard in America. The map pack will also include a new Zombies map titled Quarantine, set in Area 51, the highly controversial military base in Nevada. The map pack is set to come out in early September