Owain of Rheged comes good and rides heroically in a Theoden-like manner to the help of Pict-besieged Bamburgh! Loyalties are confused because the king of Lothian has some Pict followers who look at everything from a matrilinear perspective, whereas the British are patrilinear, and although everyone knows this, it's still hard for them to understand each other! Healing happens not just with 'herbs' which magically make everything better - but with specific, named herbs with specific properties! And the healer is very conscious of all the stuff she can't fix, and the difficulty of measuring an accurate dose!
(This is probably the kind of thing where many people will be thinking 'who cares!' but I do love heroic rescues and accidental cultural mixups and accurate herb-descriptions.)
I can't remember feeling this conflicted about a set of books... probably ever. If only the characterisation /plotting was different! I love the worldbuilding so much, but...