Accomplices miscreants initially employed in foreign prince’s terrain (8,2,5)

'accomplices' is the definition.

'miscreants initially employed in foreign prince's terrain' is the wordplay.
'initially' indicates taking the first letters.
'employed in' is an insertion indicator.
'foreign' indicates anagramming the letters (foreign order of the letters).
The initial letter of 'miscreants' is 'm'.
'princes'+'terrain'='princesterrain'
'princesterrain' with letters rearranged gives 'partnersincrie'.
'm' put inside 'partnersincrie' is 'PARTNERS IN CRIME'.