Crossword Genius

Historic hero in the plain clothes department (3)

Ross

I believe the answer is:

cid

I'm a little stuck... Click here to teach me more about this clue!

'historic hero' is the definition.
'cid' can be an answer for 'hero' (I've seen this in other clues). I'm unsure of the 'historic' bit.

'plain clothes department' is the wordplay.
'plain clothes' becomes 'ci' (I can't justify this - if you can you should believe this answer much more).
'department' becomes 'd' (abbreviation eg in MOD Ministry of Defence).
'ci'+'d'='CID'

'in the' acts as a link.

Can you help me to learn more?

I've seen this clue in the Evening Standard.
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