this pick is from my Music-Themed list of Crime novel suggestions; it's from 1947 originally, and incidentally, I am not reading a Large Print edition...but I don't know how to add this old Signet paperback edition to BookLikes, because it is too old to have an ISBN # of any type, and those are required fields when adding a book or an edition.
anyway, I suspect the "whispering master" may be a master recording with strange sounds on it, given that it is a Crime novel with a music angle, but I don't actually know for sure yet. plus it seems the killing takes place in a hotel, one of my fave locations for skullduggery. we shall see.