Investigation for leading characters in Brief Encounter (5)
I believe the answer is:
probe
'investigation' is the definition.
(probe can mean an investigation or inquiry)
'for leading characters in brief encounter' is the wordplay.
'for' becomes 'pro' (as in being 'pro' or in favour of something).
'leading' is a charade indicator (letters next to each other) (some letters go in front of others).
'characters in brief encounter' becomes 'be' (I am not sure about this - if you are sure you should believe this answer much more).
'pro'+'be'='PROBE'
Can you help me to learn more?
(Other definitions for probe that I've seen before include "Explore, examine" , "Spacecraft; investigation" , "Question or examine thoroughly" , "Poke into" , "Question or examine closely" .)