From the file's introduction
To most people, the word “winning” means completely subduing a foe. But victory need not be measured in such absolute terms. Some goals can be achieved merely by holding the opponent at bay for a long enough period of time.
When the goal is to hold off rather than physically overcome an adversary, the best tools are misdirection, obfuscation, outright prevarication, and any other techniques that can send the foe down the wrong track for a time. But when the clock is ticking, a good delaying tactic can be just as effective. Crossing the Line pits the heroes against an opponent whose goal has nothing to do with actually beating them. All this particular foe wants to do is keep them from going through the front door.
This adventure can be set in practically any locale. In fact, the details depend entirely on the backstory to which you (as GM) attach it. The antagonist, Remi Leone, should be able to apply his tactics to any desired location with only minor variations.
While Crossing the Line constitutes a complete adventure in its own right, it is best used in combination with another scenario. On his own, Remi Leone is unlikely to have sufficient motivation to interfere with the heroes, although you could certainly orchestrate a situation in which he does. As a gun for hire, though, he is more than happy to use his skills in the service of someone who has a more antagonistic relationship with the heroes.
A Short d20 Modern Adventure for Four 19th-Level Characters