Consider a boy. His name is Vasilli Ivanovich Bardeish. He has a weak chin, and jug ears which stick out sideways from his head. In May 1951, he is 22 years old.

Vasilli has had the great misfortune to be born in Ukraine in 1929. To two vicious totalitarian dictators he is just a speck of clay, to be pummelled and trampled until he has become moulded into the stuff of their utopian visions. It is a miracle that he is alive in 1951. He has been through a famine, a dekulakisation, a Great Terror, a devastating war. He has been taken prisoner, languished in camps, laboured in fields far from home. He has been an unhappy exile.

He has been promised a chance to fight back. To go home. He has been trained to work a wireless, and taught a series of secret codes. He has been given the rudimentary skills to jump out of an airplane in the dark. He has been flattered and sweet-talked by his British recruiters, who make notes on his weak chin, and give him a letter to carry to the partisans in his homeland. The letter talks of cooperation between Western intelligence and the men and women of Ukraine who do not want to be clay, not any more. The letter finishes with an exhortation that will become horribly familiar to the world in another war, seventy years later: Slava Ukraini! Glory to Ukraine!

Vasilli does not know that he will be betrayed by the Soviet spy Kim Philby.

Kim Philby, writing about the incident years later in his memoir, described his leaking of this top-secret mission – one of his last acts of homage to Stalin: ‘I do not know what happened to the parties concerned. But I can make an educated guess.’

When I set out to write a history of the Cambridge Five, one which emphasises their victims, and their role in Stalin’s strategic vision, I wanted to move beyond Philby’s blasé guesses. I wanted to track down the parties concerned, to rebalance the leger. The Five’s betrayals have been portrayed as crimes against ideas which have become unfashionable – patriotism and loyalty and duty. Their treachery was a heist on an establishment which deserved to be embarrassed. Their idealism was washed with glamour. No-one knew the depravities of Stalinism when these clever, brilliant young men were seduced by clever agents, or so the story goes.

Now consider another young man at the age of 22. Kim Philby. He has graduated from Cambridge, but failed to get into the Foreign Office. His mapped-out future has receded, and he is a little lost. He has come back from Vienna, where he saw revolutionary blood on cobbles. He has brought a wife with him, Litzi, in a union rooted in passion, Marxism and the utility of a British passport.

In June 1934, when word is already leaking out of the Soviet Union about the horrors of famine and the slave labour of the prison camps, 22-year-old Philby meets Arnold Deutsch, an illegal Soviet agent. Recruited by Deutch, Philby throws himself into the cause. The monstrous tales coming out of the Soviet Union are just bourgeois bleatings, the product of an old morality that does not understand the demands of revolution. As a journalist in the Spanish Civil War he worships his Soviet handler, the very man sent by Stalin to Spain to persecute the non-Bolshevik left.

When the Terror takes his handlers, and feeds them to the meat grinder, Philby has to work hard to get his secrets to the Soviets. When Stalin signs his pact with Hitler, Philby remains wedded to his cause. As the British fight a doomsday war against the Nazis, Philby feeds secrets to Hitler’s ally. After the German invasion of the Soviet Union, Stalin’s crimes are deliberately forgotten in the West. Propaganda washes him clean. Only when the Grand Alliance breaks down will old crimes be discovered as if they are new ones.

When the war winds to its close, Philby, now embedded in SIS, is put in charge of Soviet counter-intelligence. It is Philby’s job to understand the nature of the Soviet world. He interrogates prisoners, makes contacts with partisan groups and émigrés. He hears the stories, first hand. None of the facts, the stories of brutality and terror and hunger, can tarnish the glorious vision he holds in his head.

By the time Vasilli Bardeish climbed aboard the aeroplane in May 1951, Philby had been working relentlessly for Stalin for 17 years. He had betrayed countless other missions. Albanians, Poles, Lithuanians, Latvians, Estonians. His handler, Yuri Modin, said: ‘we knew in advance every operation that took place by air, land or sea, even in mountainous or inaccessible regions.’

Sometimes he just gave names. Sometimes precise landing details. He was put in charge of liaising with American intelligence, which was running its own extensive operations to land displaced men into their former homes. Philby betrayed those too. Soviet counter-intelligence used their incredible source to help run audacious operations to fool British and American intelligence. They played so-called Radio Games, where they forced captured agents to send messages back to the Western agencies. Send more money, more arms, more men.

On 14th May 1951, Vasilli Bardeish boarded an aeroplane in Cyprus. He was one of sixteen Ukrainians trained for the mission. The British recruited from the prisoners of war stranded in the UK, the majority of whom had served in the Galicia Division of the Waffen SS. The Americans disapproved of using men implicated in Nazi war crimes, but the British were less squeamish. Vasilli had only been 14 when the Division was created in 1943. Another boy in his team, Petr was even younger, only 12 at that time and 20 years old as he boarded the plane.

There were three groups on two planes leaving Cyprus that night, flying to the borderlands between Soviet Ukraine and communist Poland. As they flew into Soviet airspace, they saw a white flare in the sky. This was probably a signal to let them pass. The Soviets wanted the planes to reach the drop zones. They were waiting.

The first team to jump seemed to land well. But they did not make contact as ordered. They disappeared. Suddenly, at the end of July, they resumed contact and, when prompted, sent an anodyne message about their landing. They passed the pre- agreed security checks. The British description of the radio message from western Ukraine said, ‘Much of it was stating the obvious, and therefore of no great value.’ Soviet intelligence almost certainly controlled the information coming from the group. Their behaviour followed the pattern of how the radio games were played, with long silence followed by banalities.

The second team dropped into the forests. One of the team went find the local partisans. On his return, he found signs of fighting and all his comrades had disappeared. He managed to escape overland across the border, traumatised. In a subsequent debrief, his British handlers concluded that the army must have been on spring manoeuvres in the area, ‘since it is doubtful whether troops could have been on the spot so quickly had they been alerted as a result of the reported presence of an aircraft in the neighbourhood’. The full account of the mission, and subsequent debriefs are in the archives of the Central Intelligence Agency.

The third team was Vasilli’s. At first, they were lucky. Or perhaps unlucky. But Soviet counterintelligence, forewarned of their arrival, were hunting them relentlessly through the forest. By June 1951, they were all dead. Local villagers were made to parade in front of their bodies. Children were told to mark the faces of the traitors, to look into the faces of jug-eared Vasilli and blonde, handsome Petr, and learn the cost of betrayal.

While Soviet intelligence was hunting down Vasilli and Petr, the Cambridge Five spy ring had spectacularly imploded. Donald Maclean and Guy Burgess defected to the Soviet Union on 25 May 1951, Suspicion fell immediately on Philby, and slowly on Anthony Blunt and John Cairncross, the other members of the ring.

Before the Cambridge Five stopped supplying Stalin with secrets they had all contributed to Stalin’s grand strategic vision, of pushing the Soviet world out and beyond the borders of Russia. Blunt had leaked from within British intelligence, betraying the governments-in-exile of those nations who had fought to keep the dream of independence alive.

Burgess, Cairncross and, above all, Maclean, had helped Stalin win the diplomatic battles necessary to turn his military advantages into lasting control. Maclean, for example, supplied the Soviets with all the personal correspondence between Winston Churchill and Franklin Roosevelt at the war’s end, just as they were trying to work out how to deal with their troublesome ally and his grandiose demands.

Maclean’s contribution was probably more significant, but there was something particularly cruel about the blood on Philby’s hands. The covert operations across the Iron Curtain were not, on the whole, expected to bring about regime change. The role of the Western intelligence agencies was to provide military aid to the resistance, to cause mischief and collect intelligence.

The missions were modelled on the Special Operations Executive (SOE) and its World War 2 shenanigans. But like those of the SOE, these missions were supposed to have a moral weight as much as a practical impact. They were intended as a statement of intent, of reassurance to those trapped behind the Iron Curtain that they were not forgotten. There are transcripts in the Albanian and Lithuanian archives of the radio messages sent to double agents in the field by earnest American intelligence. They are full of expressions of allyship and exhortations of idealism. Behind the fine words was a gleeful Philby, sitting in the shadows, nursing a pink gin.

The Cambridge Five’s actions have been layered in myth. The part that has mattered in the popular imagination is an Anglocentric story about British society and culture. These were posh boys protected by other posh boys who betrayed a country that deserved humbling. In Stalin’s Apostles, I went back to the sources – not just in the UK and in the USA but in the Baltic states, Poland and Albania.

I asked a forgotten question: what did Stalin want from his greatest spies? And I found a boy called Vasilli about whom details are scarce. I looked for more on him, searched the records. But there are precious few words about Vasilli, and you could tap dance from London to Moscow on the words written about his dark nemesis. Vasilli is a boy lost to posterity. A boy already scarred, bone-deep, by geography and history, when he fell from the sky into a trap laid by Kim Philby.

Antonia Senior is a novelist and critic and the author of Stalin’s Apostles: The Cambridge Five and the Making of the Soviet Empire. You can listen to an interview with Antonia on the Aspects of History podcast feed.