Every town has its guard, and every guard post has its jail.

This small town has jail with several rooms: the public entrance, the storage room for seized property, the guard room with a back door, the main cells and a special cell for practitioners of magic. The glyph inscribed on the ground, coupled with the magic manacles prevent any escape, or do they?

What if one of the pcs has been caught and now is inside, how would the others try to help? What if a special subject is being kept there waiting to be transferred elsewhere and this is the only chance to get to them?