Murder by the Book (1951) is an especially fun entry in Rex Stout's long-running Nero Wolfe mystery series. Its MacGuffin is an unpublished manuscript by a law clerk, and somebody is killing everybody who has read it. If you've never read a Nero Wolfe mystery, this is a good one to start with, as the whole cast is in good form and Stout is on top of his game.
Amazon: Murder by the Book by Rex Stout.
How acquired: Picked it up from a used book store for $2.95, probably in the time since I've moved out to Michigan.