Apprehending one stranger to order (9)
I believe the answer is:
arresting
'apprehending' is the definition.
('arrest' can be a synonym of 'apprehend')
'one stranger to order' is the wordplay.
'one' becomes 'i' (Roman numeral).
'to order' indicates an anagram.
'i'+'stranger'='istranger'
'istranger' is an anagram of 'ARRESTING'.
(Other definitions for arresting that I've seen before include "Police work" , "Police officers are doing it regularly" , "Copper's work" , "Taking into custody for being eye-catching?" , "remarkable" .)