Investigation for leading characters in Brief Encounter (5)
I believe the answer is:
probe
'investigation' is the definition.
(I know that investigation can be written as probe)
'for leading characters in brief encounter' is the wordplay.
'for' becomes 'pro' (as in being 'pro' something).
'leading' says to put letters next to each other (some letters go in front of others).
'characters in brief encounter' becomes 'be' (I can't justify this - if you can you should give a lot more credence to this answer).
'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" .)