Let Fred out of durance vile at last! (5)
I believe the answer is:
freed
'durance vile at last' is the definition.
I can't judge whether this defines the answer.
'let fred out' is the wordplay.
'let' becomes 'e' (I can't justify this - if you can you should believe this answer much more).
'out' is an insertion indicator.
'e' placed into 'fred' is 'FREED'.
'of' acts as a link.
Can you help me to learn more?
(Other definitions for freed that I've seen before include "Released" , "Untied" , "Defer being liberated" , "Emancipated, let loose" .)