Divulge what they do in 'Danny, the Champion of the World' (4,3,4,4)
I believe the answer is:
give the game away
This clue is a double definition.
'divulge' is the first definition.
'what they do in danny the champion of the world' is the second definition.
(give away pheasants in the Roald Dahl story)
(Other definitions for give the game away that I've seen before include "Let slip" , "Get rid of the bag" , "show one's hand" , "resign?" , "Let cat out of bag" .)