The first game's story involved the Peregrine Falcon (PF) Squad, a small but skilled team of soldiers serving under the Regular Army's special operations division, who fight against the army of General Donald Morden in order to prevent a massive coup d'état and the creation of a New World Order. Later games featured characters from the Sparrows Unit, which is under the control of the Regular Army's intelligence division.
The player starts with only a simple handgun; as the game progresses, the player may pick up new weapons. The player can only use one weapon at a time. When a new weapon is found, it replaces the previous one. Similarly, when ammunition runs out, the player reverts to using the handgun, which has unlimited ammunition.