Overcook the fish? (4)
I believe the answer is:
char
I believe this clue is a double definition.
'overcook' is the first definition.
(I've seen this in another clue)
'fish' is the second definition.
(char is a kind of fish)
'the' is the link.
(Other definitions for char that I've seen before include "way to make carbon" , "Daily cleaner; burn" , "Burn slightly" , "Partially burn; fish" , "Make black by burning, or a small trout" .)