25% of the available players are 'singletons', operatives working alone. Each is given a mission before the game starts and each man is responsible for carrying out HIS specific mission. Enlisting any of the other operatives is fair, but you will be seperated from each other by large portions of the field because the missions will be spread out.
The remaining portion of the players are defenders. Their CO will assign them to guard different objectives which may or may not be targets of the operatives. Guards forces can be summoned from one place to another if needed, but if you move guard forces from A to B, A might be on the target list.