Policeman from Lima involved in case (4)
I believe the answer is:
plod
'policeman' is the definition.
(UK informal term for a police officer)
'lima involved in case' is the wordplay.
'lima' becomes 'L' (phonetic alphabet: alpha, bravo, charlie etc.).
'involved in' means one lot of letters goes inside another.
'case' becomes 'pod' (pod is a kind of case).
'l' put inside 'pod' is 'PLOD'.
'from' acts as a link.
(Other definitions for plod that I've seen before include "Walk doggedly" , "Work doggedly" , "grind away" , "Tramp along" , "Trudge - policeman" .)