Caroline Graham is sheer joy to read. Her characters are always eccentric but never caricatures (though the author's acerbic tongue may initially make you wonder!) The literary allusions, the author's determination to make her reader stretch (but never in a pedantic or boring way) all contribute to the "can't put it down" quality. (NEVER start a new Caroline Graham just before bedtime. Wait 'till you have several hours to spend.)
Throughout Death In Disguise I found myself sympathizing with not only the sympathetic characters, but also the obnoxious, the loopy, and the pathetic. Throughout it all the plot weaves and clues drop, which are available to the alert reader to sort out.
That said, there are some weaknesses in this particular mystery. An unfortunate affair is introduced rather clumsily for the obvious (and awkward) purpose of setting up a character's demise. The villain is only revealed through some out-of-character twists. The police work seems rather lacksadaisical, without the tightness that the excellent writing would suggest be accorded to the plot (bodies drop like ninepins and yet no crime scene is cordoned off, suspects flee without follow-up, and so on.) But the sly development of fully rounded characters plus her dead-on skewering of the new age fringe is priceless.
I'm sorry it's gone out of print. I hope the publisher plans to reissue a paperback at least. If you enjoy Dorothy Sayers, you will love Caroline Graham.