Partners & Crime, the Greenwich Village mystery bookstore, used to display a framed list of top cliches in modern mysteries. Among them, that if a mystery novel ever quotes Shakespeare, it's always from Macbeth.
My second novel, Murdering Ministers, does indeed take its title from Macbeth, but since it's about a lay minister who's murdered in a church and the full-time minister who may have done the murdering (or dun he?), I claim special dispensation from the cliche list for sheer bloody relevance. At least for the title, anyway.
But I confess, until I saw that list, it was my original intention to give all my books titles that were quotes from Macbeth, since Sue Grafton had already taken the alphabet and Janet Evanovich was advancing through the numbers. For a brief moment, my first novel was going to be called Mortal Consequences (that's from Act 5 Scene 3). I even went back and threw in some gratuitous references to the parlour game consequences -- an English form of Mad Libs, hence the spelling of "parlour" -- just to give it some extra relevance, before I realized (a) it wasn't a very memorable title and (b) at least two other authors had beaten me to it. So I took out the references, and book number one migrated to its seventh (actually, I lost count) and final title, An Embarrassment of Corpses. And it got there directly, without passing through the phrase "an embarrassment of riches" or, indeed, collecting $200.
The current book was first going to be called This Blessed Plot, but again, I was too late. Still, I'm sticking to Shakespeare, because he's an essential element of the story, which is partly set in Stratford-upon-Avon. Hence This Private Plot, lifted from one of Henry VI's parts. It works rather well -- "Private" can mean personal or isolated or secret, "Plot" can be a scheme, an area of land, or a grave-site, and they all fit the story, singly and in most combinations. So let's hope that when the book reaches a publisher, they don't have some other ideas about what to call it.