Guard in operative's Cortina (6)
I believe the answer is:
escort
'guard' is the definition.
(thesaurus)
'in operative's cortina' is the wordplay.
'in' says the answer is hidden in the clue.
'ESCORT' can be found hidden inside 'operatives cortina'.
(Other definitions for escort that I've seen before include "Ford car, first produced in 1968" , "Companion: train" , "Companion for social occasion" , "One who accompanies, for protection or as an honour" , "Protective companion" .)