F.E.A.R. Perseus Mandate is a stand-alone expansion pack to the computer game F.E.A.R. The expansion was developed by TimeGate Studios, the same development team behind the first expansion, F.E.A.R. Extraction Point.
The game follows the exploits of a new player character, a member of a secondary F.E.A.R. team sent in to investigate Armacham's Perseus Project. The game takes place during the events of the original F.E.A.R. as well as the Extraction Point expansion pack. New introductions to gameplay include friendly A.I.-controlled characters who fight alongside the player character, as well as a new faction of enemies. The sequel to F.E.A.R., F.E.A.R. 2: Project Origin, ignores the events of both expansion packs.
Source: Wikipedia, F.E.A.R. Perseus Mandate , available under the CC-BY-SA License.