On the afternoon of 22 February 1941, a small, clean-shaven, nondescript man, whom one British official described as “unattractive of appearance”, walked down an alleyway in Kabul and knocked on the back door of the Italian Embassy. Afghanistan was a neutral country, the war far away from its borders and, despite having started 17 months earlier, it was not quite a world war yet. The Nazis were supreme in Europe, with only Britain holding out.

Hitler and Stalin, having parcelled out Poland between them, were still allies. Japan had a very fraught peace with the United States where, five weeks previously, Franklin Roosevelt had been sworn in as President for his third term, having promised “the mothers and fathers of America” that “your boys are not going to be sent into any foreign wars”.

The Afghan employees of the Embassy who were gathered round the back entrance having a smoke had little reason to doubt that the man seeking entrance was anything other than a local. Like many Afghans he wore the Karakuli Afghan cap, a long shirt that came down below his knees, and flowing, loose-fitting trousers. The man’s mission was to see the Italian ambassador.

But, aware he could not just turn up and ask to see him, he told the guards he was a cook who had been sent to work for him. The guards showed him into a high-ceilinged room where the ambassador was sitting behind a large desk framed by the Italian flag and a huge picture of the Italian dictator, Benito Mussolini.

The ambassador, who was in the middle of talking to one of his Afghan employees, was more than a little upset at seeing the man. For a start he was not in a good mood. Two weeks earlier, Hitler had sent Rommel to Libya to rescue the Italians, who had been forced to flee by Wavell’s forces despite having five times more troops than the British. Like all the foreign diplomats in Kabul he dreaded unannounced visits from local Afghans, unsure whether they were spies of the government or of other embassies. He could not be sure whether this man was a spy.

His mood was not improved when the man told him he had been sent by Herr Thomas, the German who ran Siemens’ Kabul office. “What for?” roared the Italian. But instead of being cowed the man replied in a very firm and determined voice, “I don’t know. I have just been asked to see you.”

There was something in the man’s voice that made the Italian think this was no ordinary Afghan. He now had a good look at the man: he was small, but had a strong, wiry frame. The Ambassador picked up the phone and rang Thomas. For a few minutes the Italian and the German spoke, the Italian listening attentively to what the German was saying and, occasionally, murmuring. They spoke in German, which the ambassador, who was half German, knew well.

The visitor, not knowing the language, could not understand a word, but because of the way the ambassador nodded, he sensed the conversation was serious. A few minutes later the Italian put down the phone, and asked his Afghan assistant, and the servant who had brought the man to his office, to leave. As they did so the ambassador closed the door behind them, offered a seat to his visitor and, speaking slowly in English, said, “My name is Pietro Quaroni and I am the Ambassador of the Italian Legation in Kabul.”

The man then told Quaroni his name was Rahmat Khan, although, as we shall see, that was not his real name.

He was more honest when he told the Italian that he was not an Afghan but an Indian who had arrived from India on 27 January, having made the near-200-mile journey from Peshawar to Kabul on foot, through tribal territory that separated Afghanistan from British India. Khan then explained that he had not travelled alone but had acted as guide and escort to the charismatic Indian revolutionary, Subhas Bose, who had escaped from India and now wanted to go to Berlin to seek German help to free India from British rule.

Khan and Bose had established contact with the German Embassy in Kabul some weeks earlier, which is how they had been put in touch with Herr Thomas. But, despite several meetings, no firm arrangement had been made to get Bose out of Kabul. The pair were worried that the longer they stayed in Kabul the more they were exposing themselves to great danger. They had entered Afghanistan illegally, had no passport or any other papers, and had just managed to avoid being arrested by bribing an Afghan policeman.

They were convinced they could not hold out much longer and feared that if they were arrested by the Afghan police they would immediately be handed over to the British. Khan’s call on Quaroni was the last throw of the dice to make sure Bose secured travel documents which would help him cross the Afghan–Russian border and then, via the Soviet Union, make his way to Hitler’s Germany.

Unlike the Germans, who appeared to be stalling, Quaroni proved very willing. After several meetings over the next three weeks Bose, given the passport of an Italian diplomat, was escorted over the Afghan border and put on a train to Moscow, from where he took the overnight sleeper to Berlin.

There he plotted ways to free his country, met Hitler, and eventually travelled to Japan to raise an army to fight the British. He died in a plane crash days after Japan’s surrender. In India he remains a hugely controversial figure worshipped by many, some of whom still refuse to believe he died in the crash. But in many ways it was what happened to the man he left behind in Kabul, Rahmat Khan, that is an even more extraordinary story. And one that has not yet been fully told.

Within days of Bose’s departure for Europe, Khan the escort was converted into Khan the spy for the Italians.

Since the start of the war Quaroni had been trying to find a weapon with which to strike at the British in India. Having diligently followed events in the country he was convinced India was Britain’s weak link, and a blow against the jewel of the British crown would have a tremendous impact.

So when Bose nominated Khan as his agent to work with the Italians, Quaroni seized the opportunity. A few months later Khan was taken over by Italy’s Axis partner, Germany. But while Khan took money from both the Italians and the Germans he was no fascist, in fact a communist, and from the beginning was deceiving both countries.

While initially this deception game was virtually a freelance effort, once Hitler had unleased Operation Barbarossa, his invasion of the Soviet Union, Khan worked with the Russians to continue to fool the Nazis. Later still he worked for the British, who gave him the name Silver. This was a sort of British joke as there was a real Mr Silver, who was a high official based in London and involved in supervising undercover work in India.

The Germans rated him so highly that they awarded him the Iron Cross, Germany’s highest military decoration, for his services to the Reich, and gave him a transmitter which he used to broadcast directly to the headquarters of Abwehr, Hitler’s secret service, in Berlin.

He also swindled the Axis of £2.5 million in today’s money. The Germans never for one moment suspected these broadcasts were fictitious military information concocted by the British in the garden of Delhi’s Viceregal Palace. Before the war had ended he also deceived the Japanese, making him a quintuple agent, the only one of the war.

Excerpted with permission from The Indian Spy: The True Story of the Most Remarkable Secret Agent of World War II, Mihir Bose, Aleph Book Company.