In my game we are inbetween book 2 and 3. With the end of book 2 I wanted to conclude the orc section by having the PCs secure peace for Trunau with Urgir. As such they met up with Grask Uleth who began to send my players off on a series of quests to demonstrate that the people of Trunau have worth and should be protected. So yes I have gone off script a bit here.
So after the first quest things did not go so well in negotiations, some of the PCs disrespected Grask in a public forum and so he has called off peace talks. That said, this has caused discord among my players and a great deal of infighting. The player who was chief among those who disrespected Grask has now snuck into his castle. We stopped the game there as it had gone way off the rails.
So my question is, what sort of defenses should the Warlord of Belkzen have in his castle?
Urgir was once a dwarven sky citadel, so think ancient dwarven defenses being poorly maintained by orcs and their ilk.
Frankly, if you're going to introduce Grask himself and a lowbie PC disrespects him in front of his entourage, Grask would likely have stepped up and stabbed him in the face (or broken his neck with his barehands). Grask is a b@#A$$.
I wouldn't expect too many magical defenses, but lots of orcs encamped about everywhere and some nonmagical dwarven defenses that the orcs have been able to keep going. Think heavy stone or metal portals that require keys or have combination locks and the like. There are likely magical constructs as guardians, too.
All in all, not some place I would want to be in if I was a lowbie character with murderous intent. If you want to salvage the game, maybe you could have a chat with the miscreant PC and have him sneak back out quickly when he realizes he/she is in over their head? Good luck!
You could always go with the PC's intentions, and have it "leak out" that Grask was planning a double cross to kill the leaders of Trunau.
That would take out your plan of a truce. However, it would also unite your party, together with the town of Trunau, against the orcs. The PCs could even end up claiming the castle as their base once that's said and done.
That would resolve the conflict, and help them move on to slaying giants... especially if a recruiter shows up at the castle afterwards looking for the giant they heard was living there.
Hope you're able to bring your party together! Let us know how it works out.