In 1910, Vladimir Ilyich Lenin, aged 40, was living with his wife Nadya in exile in Paris, as the head of the Bolshevik group of Russian revolutionaries. The comrades would meet in a cafe in the Avenue d'Orléans , where they drank beer or grenadine and soda, and had the use of an upstairs room for lectures and discussions.
It was here that, in the autumn, they were joined by fellow revolutionary Inessa Armand. She was 36, auburn-haired and green-eyed, a member of Moscow's French community and on the run from the Russian police.
Lenin, the stormy petrel of the Social Democratic party, was facing more serious opposition than ever. His funds had been appropriated and his journal, Proletarii, closed down. Inessa Armand was fluent in four languages and had a talent for organisation. Lenin soon realised her value.
Working closely together for a common aim led in time to a love affair that was profound yet volatile. Sharing with him seven years of exile, she became his troubleshooting lieutenant. She was to help him recover his position and hone his Bolsheviks into a force that would acquire more power than the tsar, and would herself by 1919 become the most powerful woman in Moscow. Yet few people outside the small world of academic historians have heard of her, partly due to party control of Lenin's image.
The illegitimate daughter of a Parisian opera singer, Inessa had married Alexander Armand, the eldest son of a wealthy French-Russian textile family, at the age of 19. For nine years Inessa was a rich young wife, bearing Alexander four children. Then, at 28, she left him to live openly with Vladimir "Volodya" Armand, Alexander's 17-year-old brother, a university student and revolutionary.
Alexander, however, continued to maintain her and supervised the children when she was in jail or exile. When she bore Vladimir's son, Andre, in 1903, Alexander legitimised the boy. By the time Inessa Armand met Lenin, she had been imprisoned four times and had escaped from exile in Mezen, a small town on the edge of the Arctic circle. Within weeks of her escape, Volodya, who had TB, died in her arms in 1909.
The following year she joined Lenin's group. She set up a revolutionary school in Longjumeau, near Paris, where the love affair is thought to have started. She helped him rig a Social Democratic party conference in Prague, gaining by trickery a Bolshevik majority.
Nadya, his wife, offered to leave Lenin, but he asked her to stay. She agreed, but moved out of his bedroom. Nadya and Inessa were in fact friends who shared a deep faith in the revolutionary cause and in feminism. Nadya was devoted to Armand's children and even informally adopted the younger ones after Armand's death.
Inessa went back to Russia on Lenin's behalf to reorganise the St Petersburg party network, broken up by police raids. Despite her disguise as a Polish peasant, she was identified and jailed for six months.
Alexander obtained her release with a huge bail of 6,500 roubles, which, with his approval, she jumped before her trial in 1913, rejoining Lenin, who was then living near Cracow. It was there that her love affair with Lenin came to crisis.
It was Lenin who made the decision to end the affair, temporarily at least, in late 1913. This is clear from Armand's only surviving letter. "I could cope without your kisses if only I could see you...To talk with you sometimes would be such a joy and this could not cause pain to anyone. Why deprive me of that?"
He didn't. From January 1914, Lenin was to write her more than 150 letters, always with orders, but often with endnotes of guilt and sorrow, and deep concern for her. In the early war years, she lived close to Lenin and Nadya in Switzerland and Nadya wrote of idyllic threesome walks in the mountains. But Armand was starting to question Lenin. When he sent her to Paris in January 1916, under the pseudonym of Sophie Popoff, they had their one big row. He was not satisfied with her progress in raising support for him in a France locked in a horrific war, and said so. Her furious reply shocked him. "Nothing is accomplished...by using rude words," he wrote. "This is not an encouragement to further correspondence."
She only just escaped across the border in time to avoid arrest. She left him and retired to the mountains above Lake Geneva, where he bombarded her with letters and phone calls. She played with him, often refusing to answer his letters so that he had to plead with her to respond, or answering mischievously to Nadya.
After the February revolution in 1917, Armand returned to Russia with him across enemy Germany in the famous "sealed train". In October, Lenin and his Bolsheviks seized power.
The following March, Armand was appointed to the executive committee of the Moscow Soviet. That August, after a speech at Moscow's Michelson Plant, Lenin was gunned down by Fanny Kaplan, a member of a rival socialist party, escaping death by a millimetre. He sent for Armand.
"This event has reunited us and brought us even closer," she wrote to her daughter. It also won her a large apartment close to the Kremlin and included her in the new closed-circuit telephone system with direct access to Lenin. Nadya recognised the signs. She backed off, declining to accompany Lenin on his convalescence and leaving the Kremlin on his return.
By late 1918, Armand persuaded the party to accept her husband, Alexander, as a member. Soon she was created head of the women's section of the central committee, with the power to make law. But she was working 14 hours a day and the following two years were marked by civil war, famine and a terrible flu epidemic. Eventually, she succumbed to it.
Her friend Polina Vinogradskaya, just back from the front, was shocked by a visit in 1920. "Layers of dust covered everything. She was coughing and shivering. She blew on her fingers to warm them."
Lenin, just recovered himself, wrote her a stream of letters. He sent a doctor, who reported pneumonia. "You must be extremely careful," Lenin ordered, "tell your daughters to ring me daily. Tell me what you need. More firewood? Food? Who cooks for you?...Answer me, all my points. Your Lenin."
She recovered but her workload remained excessive. Lenin insisted she take a holiday, opting for a sanatorium in Kislovodsk, a resort in the Caucasus mountains. When he learned later that - despite the end of the civil war - there were "white bandits" in the surrounding mountains, he demanded that preparations be made to evacuate her.
Guests and patients were issued with rifles and summoned by siren to the party HQ during attacks. Armand mentions none of this in her diary, haunted by her own dark thoughts. She wrote of "a wild desire to be alone. I am tired even when people are talking around me . . . I wonder if this feeling of inner death will ever pass...I find it strange when other people laugh or smile . . . the only warm feelings I have left are for my children and VI [Lenin]...It's as if my heart has died."
Two members of the party committee were killed nearby and on September 14, in a general evacuation, Armand boarded a military train. They came under machine gun and artillery fire and days later arrived at the village of Belsan, where she got out in search of eggs and milk for a TB patient. There she contracted cholera. She was taken to hospital, but at midnight on September 23 she became unconscious and the next morning, as the doctor reported, "she left us".
Eight days later, in a lead-lined coffin, she arrived in Moscow at dawn. Lenin met the train with Alexander and the children. Her body lay in state all night at the House of Unions with a female guard of honour.
The next day she was buried in Red Square in a state funeral, marked by a mass singing of the Internationale . "Lenin was unrecognisable," reported Alexandra Kollontai. "At any moment, we thought he would collapse." Angelica Balabanov reported: "His whole body expressed so much sorrow...He seemed to have shrunk...His eyes seemed drowned in tears..."
Adapted from Inessa - Lenin's Mistress by Michael Pearson (Duckworth. £20). To obtain a copy for £17 plus p&p, call the Guardian book service on 0870 066 7979.