A convict turns up for the festival (4)
I believe the answer is:
gala
'the festival' is the definition.
(a gala is a festival or party)
'a convict turns up' is the wordplay.
'convict' becomes 'lag' (slang term for a prisoner).
'turns up' says the letters should be written backwards.
'a'+'lag'='alag'
'alag' reversed gives 'GALA'.
'for' is the link.
(Other definitions for gala that I've seen before include "Festive event" , "Festive occasion - variety of apple" , "Festive celebration" , "field day" , "Special sports event" .)