Managed to join detectives' rank (6)
I believe the answer is:
rancid
'rank' is the definition.
(I've seen this before)
'managed to join detectives'' is the wordplay.
'managed' becomes 'ran' (both can mean organised or was in charge of).
'to join' says to put letters next to each other.
'detectives'' becomes 'CID' (abbreviation for Criminal Investigation Department).
'ran'+'cid'='RANCID'
(Other definitions for rancid that I've seen before include "Smelling or tasting of stale fat" , "No longer fresh" , "Rotten; high" , "Foul-tasting" , "Sour like stale fat" .)