Bright university student returned with detectives (5)
I believe the answer is:
lucid
'bright' is the definition.
(thesaurus)
'university student returned with detectives' is the wordplay.
'university' becomes 'u' (abbreviation for university).
'student' becomes 'l' (as in L-plates for learner drivers).
'returned' is a reversal indicator.
'with' is a charade indicator (letters next to each other).
'detectives' becomes 'cid' (abbreviation for Criminal Investigation Department).
'u'+'l'='ul'
'ul' in reverse letter order is 'lu'.
'lu'+'cid'='LUCID'
(Other definitions for lucid that I've seen before include "Clear, easily understood" , "Sensible" , "Limpid" , "Easy to understand, clearly expressed" , "Intellectually bright" .)