After I had been meeting Blunt for a year, an obvious pattern emerged. I was able to tease things out from him - mostly pillow talk he had gathered from Guy Burgess. He claimed a writer on The Times had been approached. I traced him, and he confirmed that Burgess had tried to recruit him, but that he turned him down, fearful of the consequences of being caught. Another contact Blunt identified was Tom Wylie, a War Office clerk, long since dead. Wylie, said Blunt, used to let Burgess see anything which came into his hands. But although Blunt, under pressure, expanded his information, it always pointed at those who were either dead, long since retired, or else comfortably out of secret access and danger.

I knew that Blunt must know of others who were not retired, who still had access. These were the people he was protecting. But how could I identify them? I decided to draw up lists of all those who were mentioned by interviewees as having noted left-wing views before the war, or who interviewees felt would have been likely to have been the target for a recruitment approach from Guy Burgess.

One name stood out beyond all the others: Alister Watson. Berlin mentioned him, the writer Arthur Marshall mentioned him, Tess Rothschild mentioned him. He was, they all said, a fervent Marxist at Cambridge in the 1930s, an Apostle, and a close friend of both Blunt and Burgess. Burgess, so far as they recalled, admired him intensely during the 1930s-a sure sign that he was likely to have been approached.

I began to make inquiries into his background. I knew him quite well from the war. He worked currently as a scientist in the Admiralty Research Laboratory, and actually lived for two years with my brother in Bristol. I never cared for Watson at the time. He was tall and thin with a pinched, goatlike face and a strange affected tiptoed walk. Watson considered himself one of the greatest theoretical physicists of his day, yet most of his colleagues thought his grasp of practical work distinctly ropey and that he had made serious mistakes in theoretical work. He was, I thought, a bit of a fraud.

Watson was a failure. At Cambridge he was considered a brilliant student, destined for the highest academic honors, until his thesis was found to contain a massive fundamental error. He failed to gain a fellowship, and took a job in the Admiralty instead. After service in the Radar and Signals Establishment of the Navy, he became head of the Submarine Detection Research Section at ARL. It was one of the most secret and important jobs in the entire NATO defense establishment, but it was obscure work, particularly for one who had promised so much in his youth.

At Cambridge, Watson was an ardent Marxist; indeed, many of those I interviewed described him as the "high priest" of Marxist theory among the Apostles. Marxism had a beautiful logic, an all-embracing answer to every question, which captivated him. He was drawn to Das Kapital as others are drawn to the Bible and, like a preacher manque, he began to proselytize the creed among his friends, particularly when his hopes of an academic career began to fade. Blunt later admitted that Watson schooled him in Marxism.

When I studied his file, his departure from Cambridge struck me as most peculiar-just at the time of Munich, when radical discontent with the Establishment was at its height. It bore all the hallmarks of Burgess' and Philby's move to the right at the same period. There was one other item of interest. Victor Rothschild wrote a letter to Dick White in 1951 suggesting that Watson should be investigated in view of his Communist affiliations in the 1930s. Inexplicably, Victor's suggestion had never been pursued, and since then Watson had been successfully vetted no less than three times, and made no mention of his political background.

I decided to try Watson's name out on Blunt at our next meeting I knew it would be a waste of time to approach the matter directly, I prepared a list of all known members of the Apostles including Watson, and asked him to pick out those he had known, or felt I should take an interest in. He went down the list, but made no mention of Watson.

"What about Alister?" I asked him finally.

"No," said Blunt firmly, "he's not relevant."

The time had come to confront Blunt. I told him he was lying again, that he knew as well as I did that Watson was a close friend and fellow Communist at Cambridge. Blunt's tic started again. Yes, it was true, he admitted. They were friends. They still saw each other regularly at Apostles dinners and the like, but he had not recruited him, and nor had Guy so far as he knew.

Alister, he said, was a tragic figure, whose life had gone terribly wrong. He was a man who promised so much, yet had achieved so little, whereas his undergraduate friends, like Blunt himself and Turing, had achieved eminence, and in Turing's case immortality.

Cambridge was becoming increasingly politicized leftward by file end of the twenties. The Labour Club membership had risen to over two hundred, and there was even a vocal Communist society of thirty. While this does not prove that Blunt was a Marxist during his undergraduate years, it does indicate a far more powerful left-wing political under-current among his contemporaries than he ever admitted.

This was especially true for scientists like Alister Watson, who later joined the Cambridge Communist party. Only after Blunt's secret confession in 1963 was Watson interrogated by MI5 on suspicion that he too had been recruited by the Soviets. No confession was extracted, hut this did not lay to rest the strong suspicion that Watson, a scientist will, later worked on top-secret submarine-detection systems, had become another of the Soviet network during his Cambridge years.

In disentangling the intellectual clues that may have led both Watson and Blunt to Marx, a common factor is their undergraduate interest in the prophetic philosophy of William Blake. Watson, it turns out, wrote the lead article of the first issue of The Venture on "The Wisdom of Blake." England's eighteenth-century iconoclast painter/poet was praised fill being "the passionate enemy of the traditional ideas of the judgment of human actions and affairs by ethical and moral philosophies." According to Watson's interpretation, which Blunt later reflected in his own published study, Blake put the study of Science "beside the exercise of Art as one of the greatest objects of human life."

In the Venture article, which presumably Blunt endorsed by giving it such prominence, Watson pointed out that Blake had been pilloried "by the skeptical and leisured gentlemen of his time," whose definition of reason "did not apply to scientific investigation but to moral thought - and it is still there." This statement clearly expresses the author's strong personal conviction that even in the twentieth century the reactionary British Establishment was still prejudiced against men of science and vision.