Diabolical figure in prison no longer? (3,4)
I believe the answer is:
old nick
'diabolical figure in prison no longer?' is the definition.
I can't tell whether this defines the answer.
'diabolical figure in prison' is the wordplay.
'diabolical figure in' becomes 'old' (I can't explain this - if you can you should give a lot more credence to this answer).
'prison' becomes 'nick' (slang term for prison).
'old'+'nick'='OLD NICK'
Can you help me to learn more?
(Other definitions for old nick that I've seen before include "The Dickens" , "The Evil One" , "alternative to deep blue sea" , "cut from long ago?" , "'The prince of darkness (3,4)'" .)