Leave after prisoner finds long river (5)
I believe the answer is:
congo
'long river' is the definition.
'Congo' can be an answer for 'river' (Congo River is an example). I'm not certain of the 'long' bit.
'leave after prisoner' is the wordplay.
'leave' becomes 'go'.
'after' means one lot of letters go next to another.
'prisoner' becomes 'con' (abbreviation for 'convict').
'go' after 'con' is 'CONGO'.
'finds' acts as a link.
Can you help me to learn more?
(Other definitions for congo that I've seen before include "Brazzaville its capital" , "Second longest river of Africa" , "Former name of Zaire" , "flower" , "Africa country and river" .)