One inventor about to give away organisation's principal secret (6)
I believe the answer is:
inside
'secret' is the definition.
('inside' can be a synonym of 'secret')
'one inventor about to give away organisation's principal' is the wordplay.
I cannot really see how this works, but
'one' could be 'i' (Roman numeral) and 'i' is found within the answer.
'organisation' could be 'side' (side is a kind of organization) and 'side' is found within the answer.
A single letter 'n' remains which might be clued in a way I don't see.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for inside that I've seen before include "Interior - in prison" , "banged up" , "close to centre" , "Imprisoned" , "Middle" .)