Outstanding details can catch new detective (5,4)
I believe the answer is:
loose ends
'outstanding details' is the definition.
Although both the answer and definition are plural nouns, I cannot see how they can define each other.
'can catch new detective' is the wordplay.
'can' becomes 'loo' (slang).
'catch' becomes 'see' (synonyms).
'new' becomes 'n' (common abbreviation eg NT for New Testament).
'detective' becomes 'DS' (detective sergeant).
'loo'+'see'+'n'+'ds'='LOOSE ENDS'
Can you help me to learn more?
(Other definitions for loose ends that I've seen before include "items to be settled" , "Unfinished business" , "details yet to be explained" .)