The Cambridge spies—Kim Philby, Donald Maclean, Guy Burgess, Anthony Blunt, and John Cairncross—who burrowed into the heart of the British establishment and betrayed its secrets to the Soviet Union have been the subjects of dozens of nonfiction books and inspired numerous novels, including some by the great John le Carré. Henry Hemming, in his new book Agent M, offers the flip side of the United Kingdom’s battle with internal subversion: the story of the government moles who infiltrated Communist and fascist organizations. They have largely remained anonymous, unlike the notorious Philby and his comrades, and Hemming’s herculean efforts to link codenames to real names in British archival records are welcome, even if few people will ever find these individuals as fascinating as their traitorous counterparts. For most readers, however, the charm and interest of Hemming’s book will come from learning about the eccentric man who directed their activities.

Ian Fleming used Maxwell Knight’s moniker, M, for James Bond’s superior. Le Carré, who worked for Knight in MI5, based one of his characters on him and provided sketches for one of Knight’s naturalism books. Neither author wrote about Knight’s oddities, perhaps because in this case, reality was stranger than fiction. A highly successful spymaster who operated for years with little oversight from his nominal superiors, Knight overcame a sketchy political past and bizarre personal habits. In fact, these very attributes, Hemming shows, contributed to his success.

Born in 1900, Knight grew up with a father whose financial failure left him dependent on a wealthy uncle. Obsessed with animals, he spent long stretches observing them in the wild, rescuing injured ones, and training them. He enjoyed getting to know the personality of each animal, having a seemingly magical gift for earning their trust and affection. Following his father’s death, his uncle apprenticed him at the age of 14 to a naval training vessel. He served in the Royal Naval Reserve during World War I; never attended a university; became caught up in the jazz scene at the end of the war; housed a menagerie of animals in his apartment, including a bear named Bessie that he regularly walked through the streets; and lost a minor civil service job before, likely because of his irresponsibility, his uncle cut him off financially. Knight was adrift, working as a school games instructor, when in 1923 he was recruited by Sir George Makgill, a wealthy industrialist who had set up an intelligence organization to provide to businessmen information about Communist-inspired strikes.

Knight’s first assignment, however, was to infiltrate the British Fascisti (BF), a small, right-wing outfit, in part to identify potential recruits for Makgill’s own group. Knight was so successful that within a few months he was BF’s director of intelligence, sending operatives into the Communist party, running fascist cells in other groups, and setting up the K Society, a paramilitary wing of the BF that specialized in street fighting with Communists, kidnapping Communist leaders to prevent them from making speaking engagements, and vandalizing Communist offices.

Hemming notes that Knight shared BF’s disdain for democracy but claims he was driven more by the group’s camaraderie, hostility to communism, and British patriotism than by ideology. His loyalty to his friends from this period remained intense. Many of his old BF comrades would later work for him in MI5, infiltrating both the Communist party and the 1930s iteration of British fascism. Knight’s closest friend in BF was William Joyce, an American-born provocateur who eventually wound up in Berlin during World War II, broadcasting Nazi propaganda as Lord Haw-Haw (he was hanged as a traitor in 1946). Significantly, Joyce escaped England two days before he was to be incarcerated in 1939, following a telephoned warning from Knight.

* *

Knight was a highly successful agent runner. His work with animals had taught him how to gain the trust of naturally suspicious creatures. He knew that patiently allowing animals to make the first moves toward humans was a better tactic than approaching them. He treated all his agents like “fascinating pets,” Hemming says, making each one feel special. In Knight’s later naturalist writings his descriptions of gaining the trust of animals read like a primer on running intelligence agents—he talks about rearing “deserted or stray young birds” and “fledglings fallen from their homes, or found slightly injured.” His speaking voice—which Hemming describes as having a “gentle, firm, and reassuring tone” that “could put almost any creature at ease”—helped him nurture animals and win the loyalty of a host of spies.

Knight began working informally for British intelligence in 1929 and became a full-time employee in 1931, just as the Invergordon Mutiny in the Royal Navy—in which a thousand sailors went on strike—convinced the intelligence community that it needed his sources in the Communist party of Great Britain. His employment was not without controversy. The Home Office had qualms about employing a member of a fascist organization and considerable negotiation was required before Knight was made the head of a section of MI5 charged with obtaining intelligence about the internal Communist threat.

His section remained physically detached from the larger organization, for many years operating out of his cramped apartment (along with his assortment of pets). And Knight’s autonomy extended to his selection of recruits. Over the opposition of his superiors, Knight used a number of women, encouraging them to take secretarial and other lowly jobs in target organizations, remain inconspicuous, and, rather than push for promotion, wait to be asked to take on more important tasks. By such tactics, they slowly moved into positions of greater responsibility. The downside was that it sometimes took years for his agents to gain access to significant information—but Knight was a patient man.

That patience finally paid off in 1937 when Olga Gray, who had volunteered to work in a Communist front and slowly worked her way up, was asked by Percy Glading, a Moscow-trained liaison to Soviet intelligence, to set up a safe house in which top-secret weapons blueprints stolen from Woolwich Arsenal could be photographed. The ensuing arrests cemented Knight’s reputation in MI5. Gray’s sensational testimony at Glading’s trial led the Communists to search frantically for other government moles in their midst—a search that was itself carefully monitored by another of M’s agents who worked as a lead secretary at party headquarters.

The other great achievement of Knight’s crew was the destruction of the British fascist movement. It had morphed from the ultraconservative BF dedicated to traditional British values into a violently anti-Semitic ally of Britain’s wartime enemies, but Knight still had personal ties to some of its adherents, used them as informants, and for most of the 1930s did not regard fascism as a threat. By late 1939, however, three of his female agents had infiltrated the Right Club, a small fascist group led by Archibald “Jock” Ramsay, a Conservative member of Parliament and fanatical anti-Semite. One member of the Right Club, Anna Wolkoff, daughter of a czarist officer, was in contact with William Joyce—and, more alarmingly, with Tyler Kent, a code clerk at the American embassy, who had purloined or copied more than 1,000 confidential documents, including correspondence between Winston Churchill and Franklin Roosevelt showing FDR’s interest in aiding Britain’s war efforts. Their release could embolden American isolationists and embarrass both men. Knight arranged for the withdrawal of Kent’s diplomatic immunity; the clerk was arrested, tried, and sentenced to seven years in prison. Wolkoff got a 10-year sentence. A thousand British fascists, including Ramsay and Sir Oswald Mosley, were interned.

As Hemming notes, Knight cut a number of legal corners: An agent provocateur solicited Wolkoff to communicate with Joyce in Berlin, and Knight himself secretly broke into Kent’s apartment before his arrest to make sure the incriminating documents were actually there. When faced with a conflict between his country and some of his old friends, Knight had not hesitated.

* *

Sometimes the intelligence gathered by Knight’s agents fell through bureaucratic cracks or was ignored by his superiors. Reports that Melita Norwood, a Communist secretary, was connected to one of the Woolwich Arsenal spies were overlooked. She went on to work for Britain’s atomic-bomb project and became the longest-serving Soviet spy in the country, not being exposed until the 1990s.

When one of his agents, Tom Driberg, a flamboyant gay writer and future MP, was identified, Knight came to suspect that the leak had originated with Anthony Blunt; but again, the MI5 hierarchy dismissed his suspicions, for which he had no evidence. Still, he was prescient about Soviet espionage tactics; they had no doubt recruited spies at Oxford and Cambridge, telling them to disown communism and remain “on ice” for years. After the war, Knight warned in a report that the “Comintern is not Dead.” But within MI5 his belief that Soviet spies had penetrated the British government was ignored, and he was regarded as obsessed with communism.

Driberg also played a role in another Knight operation. When Guy Burgess surfaced in Moscow in 1956, Knight encouraged Driberg to seek an interview with him. Burgess, it was rumored, wanted to return to England and a panicked government, concluding that there was not enough legal evidence to prosecute him as a Soviet spy, feared a public-relations disaster. During the Driberg interview, Burgess gave details of some of the things he had learned while working for the British government, an offense under the Official Secrets Act. MI5 soon leaked the information to journalist Chapman Pincher, whose subsequent story, headlined “Burgess Burns His Boats. Now—and Only Now—They’ve Got Him,” ended that possibility.

Knight’s personal life was even stranger than his politics. His first love left him to marry William Joyce. His wealthy first wife, whom he met in the fascist movement, persuaded him to leave London in 1927 to run a pub in rural England; perhaps she was goaded on by having to live in an apartment with his parrot, toads, snakes, bulldog, and mongoose. The marriage was never consummated. After they lived apart for years, she committed suicide in 1936, leading her family to charge in the press that he had driven her to it. His second wife had their marriage annulled on the grounds that they had never had sex. His third wife, a member of MI5, remained married to him despite their lack of a sex life. Hemming dismisses the claim made by some writers that Knight was gay and attributes his sexual problems to a medical issue.

Astonishingly, for an intelligence operative Knight was a well-known figure in Great Britain, although not as a spymaster. During the 1950s he appeared on more than 300 BBC radio broadcasts and 40 TV shows. He wrote more than 20 books and lectured frequently on natural history. Beloved by children for his stories about the animals he had cared for, he came across “as warm-hearted, sensible, and sturdy, if at times a little stern.” He often named the animals after the agents he had run. This enigmatic man retired from MI5 in 1961 and died seven years later.

Knight’s success as a spymaster and agent runner no doubt owed a great deal to his own upbringing. He was rooted in traditional British values and mores, and was unimpressed by ideologies and abstract ideas. Even his fascist allegiances were a consequence of personal loyalty rather than ideas. Perhaps because he was so comfortable in his own skin, he was able to find and direct people who had to assume other identities and care for them for years as they played assumed parts. His agents—like the Cambridge spies—had to betray and lie to people with whom they associated. His avuncular concern no doubt made their feats of deception more tolerable. The man who loved animals but could not make love to women had a remarkable understanding of human beings.

Harvey Klehr is the Andrew W. Mellon professor emeritus of politics and history at Emory.