I don't know how easy it is to find this, but the Kindaichi Case Files is a lovely series of locked room mysteries, all very elaborate. And, all of them involve tangled relationship maps where the title character is an outsider. It's always about the r-map in these books. And in some of them, I could so see making a couple of the characters demons. (I"m thinking of #17, The Undying Butterfly, which is wonderfully twisted.)

Thanks Lisa! This gets added to my list. I'll read them for their own sake of course, but I know the question I'll bring to bear afterwards: is the elaborate detail of a locked-room crime even necessary, if one has a powerful relationship map at work? (I'm thinking of the difference between two very good Ed McBain novels: King's Ransom and Killer's Wedge; the latter includes a locked-room puzzle and the former does not, and as I see it, the latter's story is actually a bit muddied by the inclusion of the gimmick.)

Best, Ron