The Devil's Chair.
I'm a fan of B movies. Those low-budget horror tales with a cast of unknowns. Usually they are pretty badly done but sometimes you find something interesting.
'The Devil's Chair' is one such. The acting is pretty good although the old doctor overplays to Vincent Price proportions at times. There is a demon, there is a psychotic killer, there is a book of crazed lore, there is fantasy and there is a vision of the workings of a madman's mind. Oh, there's quite a bit of blood too.
It can be confusing. The plot twists come thick and fast towards the end and I can't describe them without ruining the film.
Worth a look. It certainly gave me ideas.
