It's not in Lady of the Forest; I think it might be in Lady of the Glen -- it's definitely a massacre set somewhere in Scotland, I think it's a family feud, I think it might, um, take place at dinner? Black Dinner, something like that? (There is also the complete possibility I am melding things together that do not exist or am making things up. I mean, I know my memory of it predates the Red Wedding in GRRM's A Storm of Swords, so that's not where it's coming from.)

I think I've got the first edition hardback from 1992 with the painting.

That seems like an awesome thesis topic, I'm just saying. My Chaucer professor is apparently teaching a seminar on Robin Hood this semester, which can only be awesome, I wish I was taking it.