The battle in the upcoming chapter:
Why: because Hood wants help fending off an attack.
WHY: because Hood's defensive strategy consists of meeting the enemy BEFORE they plunder the villages nearby, not defending the castle.
RESULT: Hood can fend off a big force coming to meet him, but he can't spare enough men to hold off the smaller one going after the castle from behind.

Tactical notes: the drawbridge can't be raised, and the portcullis doesn't exist. No murder holes.

Helpers: a couple of second line guards with pretty dismal equipment and whatever schroedinger equipment Anastasia and Gunther have on hand.

Oh, and Fred's lazor pistol, and Vera.