It had all the hallmarks of a classic Cold War spy caper and it began in January 1958, when British intelligence's Moscow station delivered two rolls of microfilm into the hands of the CIA's Langley headquarters.
The films showed not the blueprints for a new Soviet warplane or ballistic missile, but something potentially more powerful in the ideological war between East and West: the complete Russian text of Boris Pasternak's masterpiece, Doctor Zhivago.
In a nine-point memo, marked secret but recently declassified, British intelligence said it was "in favour of exploiting the book", warning that Soviet censors were already putting pressure on Pasternak to put out a "revised" version.
And so began a covert CIA programme to press as many copies of Doctor Zhivago, banned in the Soviet Union, into the hands of as many Soviet citizens as possible as part of a political warfare campaign against the communists. The first chosen battleground was the 1958 Brussels Expo, where both the US and the USSR had built massive pavilions to showcase their competing ways of life.
About 130 recently declassified CIA documents form the basis for a new book, The Zhivago Affair: The Kremlin, the CIA and the Battle Over a Forbidden Book, which details the extraordinary lengths the agency took to infiltrate copies behind the Iron Curtain.