One page is encrypted - it involves spies... (9)

I believe the answer is:

espionage

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'it involves spies' is the definition.
The definition suggests a singular noun which matches the answer.

'one page is encrypted' is the wordplay.
'encrypted' indicates an anagram.
'one'+'page'+'is'='onepageis'
'onepageis' with letters rearranged gives 'ESPIONAGE'.

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(Other definitions for espionage that I've seen before include "intelligence" , "secret work" , "seeking information" , "007's game" , "hush-hush work" .)

I've seen this clue in The Independent.

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