Two rather obvious conclusions leap off the pages of just about every book ever written about William Shakespeare: That his plays reflect the turbulent times in which he lived, and that very little is known for certain about his life.

James Shapiro, a much respected Shakespeare scholar and professor at Columbia University, has applied his enormous fund of Shakespearean knowledge and his zeal for historical research to these home truths in a novel way. He narrows his focus down to a single year in Shakespeare's life and teases out of the four plays that occupied the Bard in that year a number of stimulating conclusions.

As a feat of sheer scholarly research, Shapiro's book is a mind-boggling performance -- his bibliography runs to 41 pages --- and his conclusions, while obviously personal and open to debate, will make readers go back to those four plays equipped with new tools for decoding them.

In 1599 Shakespeare finished "Henry the Fifth," wrote "Julius Caesar" and "As You Like It," and shaped his first version of "Hamlet" --- four truly great plays. He was also involved in the construction of the Globe Theater (of which he was part owner) and busy acting on its stage. Offstage noises in his life (though very much onstage for most Englishmen) were the ill-fated English expedition to subdue a rebellion in Ireland, the threat of invasion from a second Spanish Armada, a host of intrigues and plots at the court of Queen Elizabeth, England's attempt to shoulder its way into the lucrative East Indies trade, and even his own domestic affairs back home in Stratford.

Dealing with all this gives Shapiro's book a divided focus. Those whose main concern is the four plays (doubtless a majority of his readers) may be impatient with the length and detail Shapiro devotes to the Irish venture and the Spanish threat in particular. There is no convenient critical pigeonhole into which to thrust this book. Call it literary criticism against a historical background. What's important is that Shapiro's perceptive research and fluent writing style make the mixture work nicely.

Of the four plays, "Henry the Fifth" is the one least esteemed by critics today. Shapiro investigates its sources and shows how it reflected England's uneasiness about the Earl of Essex and his expedition against Ireland. He concludes that it is neither pro- nor anti-war, but is rather a play about "going to war," a war that Shakespeare's audience felt was "both unavoidable and awful." "Julius Caesar" he sees as a clever blending of religious and political concerns then prevalent in English society.

He finds "Hamlet" remarkable for many reasons beyond its sheer greatness as literature. Here, Shapiro says, Shakespeare brought a new depth and style to the stage soliloquy, a form he finds based on the then-new art of the personal prose essay. For Shapiro, Hamlet is a man who "needs to talk, but there is nobody in whom he can confide" --- except his audience. Shapiro is also captivated by Shakespeare's verbal virtuosity in "Hamlet," where he uses about 600 words never before used in any of his plays and about 170 words or phrases that he "coined or used in new ways."

"As You Like It," the only comedy among the four plays, might seem harder to relate to the author's times, but Shapiro gamely tries, finding reflections of England's rural problems in the forest of Arden and the melancholy philosopher Jaques Shakespeare's first try at writing satire. Mainly though, he finds in this play a new and deeper form of comedy, built around Orlando's education in what love really is.

These literary judgments rest on a thick underpinning of historical information, assessment of Shakespeare's sources, the writings and activities of his contemporaries, and the tangled web of intrigue around the aging Queen Elizabeth. Shapiro weaves it all together expertly, and for good measure throws in a good deal of astute textual criticism, showing how words we think we know today really meant something quite different to Shakespeare ("jig," for instance). Most modern stagings and editions of "Hamlet" he dismisses as "incoherent" versions that Shakespeare "neither wrote nor imagined."

This is not a book for the casual reader, but those with a genuine interest in Shakespeare and his times will find it endlessly rewarding.