At the end, could anyone joining organised crime leave the ranks? (5)
I believe the answer is:
demob
'leave the ranks?' is the definition.
(leave military ranks)
'at the end could anyone joining organised crime' is the wordplay.
'at the end' says to take the final letters.
'joining' means one lot of letters go next to another.
'organised crime' becomes 'mob' (as in the mafia).
The final letters of 'could anyone' are 'de'.
'de'+'mob'='DEMOB'
(Other definitions for demob that I've seen before include "Retire from military service" , "Discharge soldiers (abbr.)" , "stand down" , "Release from army" , "disbandment" .)