As the description states, “When characters discover a castle in the wilderness they will be unsure of the type of reception they will receive.” [X59] The encounter assumes A) the DM doesn’t have an attitude/reaction planned for the patrol and B) “the party does nothing either to arouse suspicion or inspire trust.”
The nature of the patrol (heavy or medium horse) depends upon the type of ruler (NPC class), but that’s a minor detail. Although I love the fact that it states “Note that the men listed are only part of the castle owner's forces. The rest of the force should include men and might even include special creatures such as trolls, or combinations such as superheroes mounted on griffons.”
I get chills.
The meat of this section are the possible reactions. Rather than the full monster reaction table, there are three basic possibilities: Pursue, Ignore, or Friendly. There is no CHA modifier (these are professionals), though I would probably allow a re-roll if the players showed some good role-playing.
Pursue: This isn’t necessarily a chase (though it could be). It could be a toll charged. Refusal can result in a fight or arrest.
Ignore: Just as it says. They pretty much give the PCs a “Move along.” It’s important to remember the ‘nothing to arouse suspicion’ caveat earlier here. PCs can act and look pretty suspicious sometimes without really trying!
Friendly: An invite of the keep’s hospitality. A fun tidbit: This can be offered by bad guys “for evil purposes” (!) Awesome.
A final note regarding demi-humans mentions “Elves, dwarves, and halflings are not given on this list, as their strongholds are special cases.” and suggests they would avoid contact. Fair enough, but that might vary from setting to setting.
So imagine the scenario of the PCs cutting cross-country, entering the territory of a 13th level wizard’s tower. It’s late afternoon and a patrol of a half dozen heavy horsemen appear. They are not hostile and even suggest the PCs might wish to shelter at the tower for the evening. The magus is always happy for guests. If they accept, maybe they come to the tower to find a bugbear mounted on a manticore is guarding the gate and lets them and the patrol enter without fuss.
Is the wizard evil? Are the PCs in for a really bad time? What would happen if they refused the offer? Maybe the mage is benign and he could even become an ally or resource for the party. All because they took a wrong turn at that gully and went one hex off-course.
Man, I love this game!