Biography is a sedate genre. Biographers are plodders. They accumulate facts and order them chronologically. Biographers are fair and objective and no fun. They are the grubbers of literature. The word most often used for the competent biographer is “workmanlike.”

Of course, biographers have tried to jazz up the genre. Justin Kaplan, author of acclaimed biographies of Mark Twain and Walt Whitman, aspired to literary distinction. So he violated chronology to begin his biography with the dying Whitman. Leon Edel liked to use flashbacks and other novelistic techniques. Actually, any close inspection of the best biographies would call for a retraction of my first paragraph.

Enter Antony Beevor with a biography in the form of a mystery story. This novelty makes for exciting reading – the interpretation of tantalizing clues, the search for secret dossiers, and a good dose of paranoia as the biographer threads his way through the murderous duplicities of Stalinist Russia and Hitlerine Germany.

But a biography is not a mystery story, really, because mysteries are melodramas – the confrontation of good and evil, the crime-solving, the apprehending of a criminal, the triumph and sometimes the vindication of the hero-sleuth. In other words, the world Mr. Beevor explores is too complex to provide a definitive answer to his book’s subtitle’s question: “Was Hitler’s favorite actress a Russian spy?”

It is to Mr. Beevor’s credit that he does not try to force his evidence to fit a neat formulaic conclusion. Unsolved mysteries can be more intriguing than solved ones, provided the writer enhances our appreciation of the mystery itself and the ambiguous world his characters inhabit.

Olga Konstantinova Knipper came from a family of German origins, the Knippers, who married into the family of famous playwright Anton Chekhov. Olga’s mother disapproved of her beautiful daughter’s desire to be an actress even after Olga married Mikhail Chekhov, a brilliant actor and acting teacher (Marilyn Monroe was one of his students) and the playwright’s nephew.

The marriage failed. Mikhail was a drunk. Olga in her 20s was a mother without a profession. Come the revolution and the bloody Civil War (her brother Lev fought on the side of the Whites), Olga suddenly left the Soviet Union for (she said) a six-week stay abroad but remained away from her native land for 25 years, becoming a German film star, and one of Goebbels’s favorites (it is doubtful, as Mr. Beevor has to admit, that she was a Hitler confidant).

Olga was a world-class liar. In her autobiography, she gives herself roles in Stanislavsky’s famous productions when in fact she never performed once on a Russian stage. In another improbable scene, she relates how she deflated Goebbels’s boasts that Germany would conquer Russia. As Mr. Beevor observes, it is hard to believe that she actually threw the ex ample of Napoleon’s fate into the propaganda chief’s face.

But what Chekhova accomplished is more remarkable than her vain lies. Not only did she become an international star in the silent era of film, she successfully made the transition to talkies, survived the Soviet invasion of Germany, and returned to Russia under the special protection of the Soviet intelligence services.

This was an extraordinary life, which Mr. Beevor handles with disciplined speculation. He would seem to be at a disadvantage, as he was refused permission to peruse Soviet archival records. But the circumstantial evidence is overwhelming. On some level, Olga Chekhova was a Soviet operative.

How else to explain not merely her survival but her triumph? Coming from a German family, she should have been marked for elimination. To be out of the Soviet Union during the war was enough to earn a one-way ticket to a labor camp. What is more, Olga remained in contact with her family throughout World War II – an astonishing fact in itself for a woman who was photographed with Hitler and entertained German troops.

Such facts only deepen the mystery. What could Olga Chekhova possibly have told Soviet intelligence that made her such a valuable property? Mr. Beevor cannot answer the question, but my own supposition, based on Mr. Beevor’s brilliant portrayal of Chekhova’s character, is that she told them more than she knew. She seduced her Soviet spymasters into believing they had a mole.

The history of spying is such that spies and their masters turn out to be as gullible as those they surveil. Surely this is one lesson to be learned again from the Iraq War – itself provoked in part by seasoned professionals who wanted to believe they had inside sources on Saddam. If Mr. Beevor was not able to gain complete access to Soviet archives, it may be because they would tell him less, not more, about her activities. Let’s not forget that a former KGB man runs Russia today.

This splendid biography turns out to be about much more than just one mysterious woman. The world of acting and the world of spying are both make-believe worlds. Olga proved useful to the Nazis because, in Mr. Beevor’s words, she made the regime “more acceptable internationally.” At one point, her prestige was so high that Soviet agents thought she could be used in an assassination plot against Hitler.

The idea of using Chekhova as a weapon is far-fetched, and Mr. Beevor doubts that the actress ever knew about this plan, but it shows how important her role was in the fantasies of agents like those who later thought they could kill Fidel Castro with an exploding cigar.

Mr. Beevor wonders about all the compromises Chekhova had to make in order to satisfy both her Soviet and Nazi controllers. No doubt she had her rough moments. But as an ex-actor myself, I have to think that she reveled in the role of a lifetime – playing one side against the other while preserving the mystique that made her so desirable to a world audience.