I'm on a nonfiction binge right now.
Right now, I'm reading Dennis McCarthy's Thomas North: the Original Author of Shakespeare's Plays.
Yes, there are a lot of theories about someone other than Shakespeare being the author of the plays, and up until now, I haven't found any such theory persuasive. But Dennis McCarthy, using forensic linguistics (computer based language comparisons), has produced a large body of evidence that Thomas North is the primary author of almost the entire Shakespeare canon.
It's been known for a long time that Shakespeare's Roman plays borrowed heavily from North's translation of Plutarch's Lives, including lifting whole passages almost verbatim, but McCarthy provides hundreds of other parallels with North's various works. Much of the language is unique or almost unique to North and Shakespeare. Even more tellingly, Shakespeare's plays borrow from unpublished works by North, such as his travel journal.
As if the linguistic evidence is not enough, McCarthy also provides convincing biographical evidence linking North's life to the substance of the plays, providing evidence that North wrote plays (now lost) that Shakespeare adapted (including the Ur-Hamlet) and that Shakespeare's contemporaries were aware his plays weren't all that original.
McCarthy's theory is that North, fallen on hard times, sold his plays to Shakespeare about 1591 (shortly before Shakespeare's "own" plays began to be performed).
If you're less interested in evidence for such a theory and more interested in how McCarthy accumulated clues, try Michael Blanding's In Shakespeare's Shadow, which takes about how McCarthy accumulated his clues.
