There is an echo of foxy, seductive Scarlett O'Hara about Moura Budberg in her epic career from pre-war aristocratic privilege in Estonia to serious hardship in post-revolutionary Russia and her deliberate policy of marrying wealthy, high-status men while remaining devoted to a married lover.

Scarlett's passion for Ashley Wilkes is a mirror image of Moura's love for the British diplomat Robert Hamilton Bruce Lockhart who claimed with Scottish pride to have "no drop of English blood" in his veins.

As a serial, sentimental womaniser, young Lockhart, then in his early twenties, had disgraced himself as a vice consul in Moscow in 1912 and was packed off home. But his political acumen, spirit of adventure and knowledge of Russia was recognised by Lloyd George who dispatched him to St Petersburg (renamed Petrograd) early in 1918 as head of a small, discreet, unofficial government mission to make direct contact with the revolutionary Bolshevik leaders Leon Trotsky and Vladimir Lenin, and open up secret communications with them. At dinner, a fortnight after arriving in Russia, he met an attractive young married woman, Maria von Benckendorff, known to everyone as Moura.

Before the revolution, Moura had maintained good relations with the British Embassy. Afterwards, in the early days of the revolution, she discreetly became the lover of the Russian premier Alexander Kerensky who, though he suspected her of working for British intelligence, relied on her as a source of high society political gossip about Russian pro-German sympathisers. He was hardly sure from one moment to the next whether she was a British, German or Russian agent. And so Moura's great game began. "Her great talent", say McDonald and Dronfield, "was the ability to play one side against the other, and gain advantage for herself: to commit treachery and make the betrayed love and forgive her." Above all, she was a spy in her own interests.

When political power began to move to Moscow, Lockhart followed it and Moura followed Lockhart. They had already flirted, and now they fell in love. It is at this point that Moura's biographers give us the first of many movie moments and money shots: "The room was aglow with midday spring sunshine. Standing near the window, her dark hair alive with light, was Moura. Lockhart paused, then walked towards her in silence, so overcome he couldn't trust himself to speak." All that this scene lacks is a music soundtrack; "Moura's theme" in the style of "Lara's theme".

By 1919, Moura's husband had been mysteriously shot in his remote dacha in Estonia, her mother had died, Lockhart after many hair-raising adventures had been moved to the British Legation in Prague, and Moura, who for various reasons had married the rakish young gambler Baron Nikolai Budberg in Estonia and then packed him off to Rio de Janeiro, had become a sort of amanuensis and lover to Maxim Gorky, the Russian author, political activist, founder of socialist realism.

Through Gorky she met the writer HG Wells on his post-revolutionary fact-finding trip to Russia. Wells hired her as his official interpreter, and how could these two charismatic, promiscuous personalities not fall fatally for one another? In time, Moura would gain a visa for England, become one of Wells's long-term lovers and make a life for herself as a grande dame in the social, cultural and political life of London.

McDonald and Dronfield are as much mesmerised as mystified by Moura. Even Moura's daughter Tania could never fathom "how someone who had suffered as much, and lost as much, as my mother, could still expect and command such adulation". Late in life, living in England, Moura took a British publisher's shilling more than once on a promise to write her story, but these memoirs, by no means fully written and more than probably misleading, were destroyed, along with many other important documents, including some belonging to Gorky but appropriated by Moura, in a fire shortly before her death in 1974.

To suspicions that she had colluded in the shooting of Djon von Benckendorff, her first husband, and of having connived in the poisoning of Gorky in 1936, add an implication that, if she did not set fire to her own papers, she certainly did nothing to stop them being incinerated and finally covering her tracks literally with smoke. She owed loyalty to no-one but herself.

If, as the authors say, Moura retrospectively aggrandised herself and didn't worry about distinguishing fact from fiction, "what she was really doing was creating an artistic truth for herself". In this richly romantic biography they also create an artistic, novelistic effect in the telling of her story as, perhaps, she might have liked it to be written. It would certainly have amused her as much as it will entertain the reader.