Month’s work’s involved in unknown film (9)

I believe the answer is:

octopussy

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'film' is the definition.
(I've seen this before)

'month's work's involved in unknown' is the wordplay.
'month's' becomes 'oct's' (abbreviation for October).
'work's involved' becomes 'opus' (I can't justify this - if you can you should believe this answer much more).
'in' is an insertion indicator.
'unknown' becomes 'y' (algebra).
'octs' going around 'opus' is 'octopuss'.
'octopuss'+'y'='OCTOPUSSY'

Can you help me to learn more?

(Other definitions for octopussy that I've seen before include "Bond film with Roger Moore (many-tentacled cat?)" , "1983 James Bond film" .)

I've seen this clue in The Times.

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