Clandestine second party serving men (4-4)

I believe the answer is:

back-door

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

'second party serving men' is the wordplay.
'second' becomes 'back' (to second a motion is to back it).
'party' becomes 'do' (do is a kind of party).
'serving men' becomes 'OR' (military abbreviation for Other Ranks).
'back'+'do'+'or'='BACK-DOOR'

I've seen this clue in The Guardian.

Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.