Fall of scoundrel involved in case (7)
I believe the answer is:
cascade
'fall' is the definition.
(cascading is a kind of falling)
'scoundrel involved in case' is the wordplay.
'scoundrel' becomes 'cad' (cad is a kind of scoundrel).
'involved in' is an insertion indicator.
'cad' put inside 'case' is 'CASCADE'.
'of' acts as a link.
(Other definitions for cascade that I've seen before include "Shower" , "Dramatic fall" , "Small waterfall or series of them" , "Waterfall or deluge" , "Torrent" .)