Shapiro makes clear from the start that he believes in the traditional narrative, that Shakespeare of Stratford wrote the plays attributed to him (though, he points out, we must make room in that narrative for recent findings about collaboration and co-authorship in the case of several of the canonical works). The book is partly a defense of the Stratfordian position, but it is also a trenchant examination of how there got to be a debate in the first place. Shapiro delves deep down into the roots of the authorship controversy; these are, we learn, surprisingly shallow - when forgeries are removed from the picture, it's not until the middle of the 19th century that questions about Shakespeare's identity began to percolate ... a trend that's gained much steam with the rise of the Internet.
But there was an interpretive groundwork on which the authorship questions were founded, which Shapiro argues began with scholar Edmond Malone (known to us as the refuter of the Ireland forgeries, which also come into Shapiro's story). Malone's belief that Shakespeare's plays and poems should be read autobiographically is the foundation on which the entire authorship house of cards has been erected, Shapiro argues - it is this that has enable the proponents of other candidates to claim that their chosen author is a better fit (Shakespeare couldn't possibly have written so eloquently about the law because he wasn't a law, or Venice because he'd never been, &c. &c.). Shapiro warns that this is a false premise - that to read the works as if they are autobiography, we discredit Shakespeare's literary imagination, (and we fail to grasp the nature of Elizabethan and Jacobean writing styles, to boot). He finds a quote in the 1593 poem Licia that proves his point: "A man may write of love, and not be in love, as well as of husbandry, and not go to plough, or of witches and be none."
Even as he carefully, even patiently, takes apart their claims, however, Shapiro explores many of the various branches of the controversy and their proponents - Delia Bacon's near-maniacal support of Francis Bacon as the author (which came to attract the attention, among others, of Mark Twain and Helen Keller), and John Thomas Looney's advocacy of Edward de Vere, the seventh Earl of Oxford (considered by many the leading "alternative candidate" at this point). Shapiro traces the lines of argument for the Oxfordian position right up to the present, noting that while it continues to attract high-profile interest (including Sigmund Freud and prominent actor Sir Derek Jacobi, among others), the cause has failed to actually produce a single shred of hard evidence for the conspiracy they insist had to have taken place (that Will Shakespeare was de Vere's "front man"). Nothing in the contemporary literature or biographical treatments of the time suggests this, as Shapiro points out, forcing opponents of the traditional Shakespeare into linguistic and historical contortions to explain them away.
As fine and fair a survey of the authorship debate as we're ever likely to see, which comes to the only conclusion possible given the evidence we have.