You know how in cop shows the characters always seem to have episodes where they’re arguing over jurisdiction? “I’m not letting the Feds take this away from me, this is my case!” and all that. Curiously, it’s an idea that isn’t just relevant to writers of detective fiction. It should also crop up with depressing regularity in your historical fiction and vaguely medieval fantasy too.
You see, for England at least (and for lots of other places, but this is the bit I know best) there wasn’t a simple, neat chain of authority and law in the way people might expect, given ideas about the feudal system (I believe I may have made my feelings on that one clear already). Instead, there was a kind of real life Venn diagram of laws, ranging from the laws of the land, to church laws, and the many effects of custom and grants, which only served to make things even more complicated.
As for which court or other authority was the right one to hear disputes… that’s where it gets really awkward. You see, people of particular areas could be subject to particular courts thanks to charters such as the one giving the canons of Beverley the right to hear cases arising in their prebendal lands, or they might come under the roving ecclesiastical courts of the various archdeacons (who sometimes worked out of minsters like Beverley, as it happens). They could be brought before the court of a particular lord, or be up before the local magistrate, or any one of many other power figures.
They could also be exempt from particular courts. Monks, canons and other clerics were often exempt from trial in lay law courts, though the extent of that exemption could vary. Some charters relating to Cistercian monasteries set out a general exemption for everyone even remotely connected with them (down to villagers in ‘their’ villages), while extended powers of sanctuary relating to whole towns could further complicate the issue in the case of minsters.
Then there was the case of the highest courts (royal, archiepiscopal, papal, and so on). The figures behind these courts were often in a certain amount of on-going competition to extend influence over as wide an area as possible, and did so partly by accepting legal cases, thus saying ‘yes, I have legal authority there.’ The other side of this is that they could get remarkably stroppy about people taking cases to their rivals in ‘their’ areas (Archbishop Wickwaine actually excommunicated a lot of the men of Beverley when they took a case to Canterbury during the thirteenth century, when York was still trying to claim primacy in England)
The result of this was a legal system where people could almost shop around for the courts they wanted. How does that affect your story? Well, you could have a character trying to do just that, or simply mired in the complexities of a legal dispute. You could have characters showing up trying to run to a favourable jurisdiction, or complicating a situation by bringing in another power by claiming its protection. You could even have a suitably monastic detective (Cadfael anyone?) complaining about how “Canterbury is not going to use jurisdiction to take over here! This is my case, damn it! Sorry, Brother Augustine. I don’t know what came over me.”