Sidney Reilly was still in Petrograd when events turned sour. His plan to overthrow the Bolshevik Government had spun wildly out of control and he knew he would need his wits about him if he was to keep one step ahead of the Cheka.

He first realised that something was seriously awry when Captain Cromie, naval attaché at the British Embassy, failed to turn up to a secret rendezvous on the afternoon of 31 August. "Not like Cromie to be unpunctual," observed Reilly.

After waiting for another fifteen minutes at the pre-agreed location, he decided to make his way towards the embassy. It was "a dangerous move" - for he risked being searched - "but I had brought it off successfully before."

He turned into Vlademirovsky Prospect, only to be confronted by a group of men and women running towards him in panic. "They dived into doorways, into side-streets everywhere."

Reilly was perplexed as to what was happening. A military car sped past, filled with Red Army soldiers. It was heading in the opposite direction to the crowd, racing towards the embassy. Reilly quickened his pace as he reached the end of Vlademirovsky Prospect. As he turned the corner, he immediately realised that something was seriously wrong.

"The Embassy door had been battered off its hinges. The Embassy flag had been torn down. The Embassy had been carried by storm."

On the pavement outside there were several bloodstained corpses. Reilly glanced at them and noticed that they were not English. They were Russians, Bolsheviks, who he presumed to have been killed while storming the building.

It was to be some hours before Reilly discovered the grim details of what had taken place. Others had been rather closer to the action. Nathalie Bucknell, wife of one of the few remaining staff at the embassy, was in the passport office on the ground floor when she heard the crack of gunshots coming from upstairs. It was exactly 4.50 p.m. She poked her head into the entrance hall, only to hear more intense shooting and "terrible screams". She was as frightened as she was puzzled; she had not heard any soldiers entering the building.

The embassy porter crept into the hall and peered nervously up the stairwell. He motioned for her to take cover. She did so just in time. As she crouched in the small lobby adjoining the hall, a group of men could be heard careering down the grandiose staircase. At its head was Captain Cromie, wildly firing his revolver. Behind him, and in hot pursuit, were Red Guards. They too were firing their guns.

Nathalie sank to her knees in fear. There was a constant crackle of gunfire as the shoot-out intensified and bullets began to ricochet off the marble walls and columns. She peeked through the keyhole just as one of the bullets hit its target. "Captain Cromie fell backwards on the last step."

He was seriously wounded and clearly in need of urgent medical attention.

The Red Guards dashed into the street, seemingly confused by the lack of other gunmen. As they did so, a second group of soldiers came clattering down the stairs, equally dazed by the shoot-out. One of them paused for a moment to kick Cromie's half-conscious body....

Nathalie could hear the sound of yet more soldiers on the first floor of the building; they were bawling to the embassy staff who had hid themselves away in fear of their lives. "Come out of the room, come out of the room, or we will open machine-gun fire on you."

Nathalie was joined by her friend Miss Blumberg, who had taken refuge in one of the downstairs rooms. Together, the two women gingerly stepped into the hall in order to see what they could do for Captain Cromie. He was smeared with blood. "Bending over him, we saw his eyelids and lips move very faintly."

As Miss Blumberg attempted to speak to him, a group of Red Guards reappeared and started shouting insults.

Pointing their revolvers at her, they called very rudely: "Come upstairs immediately or we will fire at you."

The two women did not dare to argue; they were led up to the first floor with revolvers poking into their bodies. Nathalie saw graphic evidence of the shoot-out that had taken place. On the floor, lying in a pool of rapidly congealing blood, was the corpse of a Red Guard.

The two ladies were jostled into the Chancery room where Ernest Boyce, head of Mansfield Cumming's operations inside Russia, was being held at gunpoint. "At that moment, the Red Commissary entered and told everyone that they must keep quiet with their hands up and that the Consulate was taken by the Red Guards."

Miss Blumberg bravely asked if she could give the dying Cromie a glass of water. Her request was brusquely denied by the soldiers. The chaplain was treated with equal contempt when he asked to attend to the semi-conscious English captain.

The rest of the British staff were now brought into the Chancery and told that they were being held as prisoners. Most were still reeling from what had taken place. They knew of the assassination of Uritsky and of the attempt on Lenin's life, but only Ernest Boyce was aware of Reilly's planned coup and even he did not know that it had been exposed by the Cheka.

"The room was now full of soldiers and sailors who were most brutal in their behaviour," wrote Nathalie. The porter was led through each room with a revolver pressed to his head. The guards said they would shoot him if he did not unlock every door and cupboard.

The hostages were held for several hours while the embassy was stripped of everything of value, including all its archives and secret documents. The staff were then marched down the stairs, passing the now-dead Captain Cromie, and taken to a nearby building. For the next fifteen hours, they were held prisoner and interrogated, one by one.

Nathalie overheard a soldier saying that five of them, including Boyce, were going to be shot. But the executions were inexplicably annuled before they could be carried out. At 11 a.m. on 1 September, all of the prisoners were informed that they were free to go. Bewildered as to why they were being released, but not daring to ask any questions, they gratefully made their way into the street.

In England, the murder of Cromie on the sacred premises of the British embassy provoked universal outrage and an ultimatum from the War Cabinet threatening extreme action if any further harm came to British subjects. "His Majesty's Government", quoted the front page of Ransome's own newspaper, "will hold the members of the Soviet Government individually responsible, and will make every endeavour to secure that they shall be treated as outlaws by the governments of all civilized nations, and that no place of refuge shall be left to them."

Ransome himself appears to have been stunned by the news, and at first could scarcely credit it. He had liked Cromie. They had played chess together. There was no man more noble or constant. Cromie, he insisted, had been a true friend to the Soviet, one of the very few capable of inspiring trust on both sides of the ever-widening divide. His loss was a tragedy, a dreadful error, whereas the arrest of Lockhart approached farce. "The papers here", Ransome told the Daily News, "print today the story of an Entente conspiracy against the Soviet government which outdoes any sensational novel in both complexity of plan and wildness of detail. Some details are so fantastic as to cast doubt on the whole, and the whole so impracticable that I find it hard to believe it was ever seriously considered."