Castle Bouttreaux is the westernmost holding of the French lord Guillame de Averoigne. Although nominally a vassal of King Stephen, Lord Guillame is one of those scheming middle-of-the-road types that has so far avoided committing seriously to either side in the Anarchy. That and the relative poverty of the region (dragonfire keeping property values down) has thus far kept the region free from warfare in these troubled times.
Lord Guillame has never actually visited Cornwall (or England proper for that matter), so the local ruler in all but name is his hand-picked man, William of Crevan. Sir William is known for being a fair-minded steward. He does not think much about "that gang of robbers" staying at the Abbey of St. Emmet or the upstart Sir Hugo and his den of iniquity, but you PCs and your followers are so weird and numerous he has so far avoided a direct conflict. Also, he does not want to annoy the Abbot, whom he respects, or Hugo's liege Lord Sutcherly, whom he fears.
Other notable inhabitants of the castle:
Lady Chezmerelda - Lady Susan's rather frumpy older sister. A widow with estates in the north. Newly arrived in the area just a few weeks ago. Rumor has it that she and Sir William are not on the best of terms and that all the hunting he's been doing lately has been to get himself out of the house.
Father Andrew - The castle chaplain. He considers it a point of professional honor to be sober enough to give the Mass on Sunday. Any other day he's usually soused.