Scoundrel breaks into song in rural paradise (7)
I believe the answer is:
arcadia
'rural paradise' is the definition.
(I've seen this before)
'scoundrel breaks into song' is the wordplay.
'scoundrel' becomes 'cad' (cad is a kind of scoundrel).
'breaks into' is an insertion indicator (inserted letters break into the word).
'song' becomes 'aria' (aria is a kind of song).
'cad' going within 'aria' is 'ARCADIA'.
'in' acts as a link.
(Other definitions for arcadia that I've seen before include "such as Strephon enjoyed?" , "Tom Stoppard play" , "rural area" , "pastoral country" , "Ideal rustic paradise" .)