Try Polanski film including line without mercy (9)
I believe the answer is:
heartless
'without mercy' is the definition.
(thesaurus)
'try polanski film including line' is the wordplay.
'try' becomes 'hear' (as in to try someone in court or hear their case).
'polanski film' becomes 'tess' (I've seen this in another clue).
'including' indicates putting letters inside.
'line' becomes 'l' (used when specifying particular lines from a poem).
'tess' placed around 'l' is 'tless'.
'hear'+'tless'='HEARTLESS'
(Other definitions for heartless that I've seen before include "hard?" , "Unkind" , "Scrooge was" , "Uncaring" , "Without pity or feeling, being defective in cardiac way" .)