A convict returns for the festival (4)
I believe the answer is:
gala
'the festival' is the definition.
(a gala is a festival or party)
'a convict returns' is the wordplay.
'convict' becomes 'lag' (slang term for a prisoner).
'returns' shows that the letters should be reversed in order.
'a'+'lag'='alag'
'alag' written backwards gives 'GALA'.
'for' acts as a link.
(Other definitions for gala that I've seen before include "Special social or sporting occasion" , "field day" , "Mix" , "Prod with the elbow" , "Special festivity" .)