Meet again about detaining prisoner in flat (9)
I believe the answer is:
reconvene
'meet again' is the definition.
('convene' is an answer for 'meet' so perhaps 'reconvene' is OK for 'meet again')
'detaining prisoner in flat' is the wordplay.
I cannot quite understand how this works, but
'prisoner' could be 'con' (abbreviation for 'convict') and 'con' is found within the answer.
'flat' could be 'even' (similar in meaning) and 'even' is present in the leftover letters.
The remaining letters 're' is a valid word which might be clued in a way I don't see.
This may be the basis of the clue (or it may be nonsense).
'about' is the link.
(Other definitions for reconvene that I've seen before include "Meet again" , "get together again" .)