In the shadowed history of Cold War espionage, the Cambridge Spy Ring has long been remembered as a circle of five: Kim Philby, Guy Burgess, Donald Maclean, Anthony Blunt, and John Cairncross—gifted men shaped by Cambridge who passed British secrets to the Soviet Union. But what if there was a sixth? What if another operative, known only by the code name “Cuthbert,” moved among them undetected, hidden in plain sight?
According to this provocative investigation, Cuthbert was recruited alongside the others in the 1930s, amid the anti-fascist zeal and left-wing idealism of Cambridge. Unlike Philby and Burgess, whose notoriety later defined the scandal, Cuthbert remained in the margins: a sleeper agent who fed disinformation, facilitated escapes, and helped preserve the network without ever attracting suspicion.
The mystery deepens in 2024, when a memorandum discovered in a Moscow archive appears to reference an unnamed sixth asset linked to the 1951 defections of Burgess and Maclean. Though the document contains no photograph or full identification, its cryptic language reignites old suspicions. Had historians, biographers, and intelligence officers missed a deeper layer to the story? Was the famous search for the “Fifth Man” only part of a larger deception?
Drawing on newly surfaced Russian files, overlooked MI5 interrogations, decrypted signals, and interviews with aging Cold War witnesses, The Last Spy: The Unmasking of the Sixth Man reconstructs Cuthbert’s possible path—from Cambridge debating societies to wartime London and postwar Europe, where subtle interventions may have helped shield the ring from collapse.
As the evidence accumulates, the book examines omissions in Philby’s memoirs, anomalous wartime communications, and a roster of possible suspects, from diplomats to well-connected intellectuals. Blending the suspense of a spy thriller with the texture of archival scholarship, it builds toward a startling conclusion: that the Cambridge ring may never have been five men at all, but six—and that its last secret remained hidden for decades.