Look into quiet villain's introduction (8)
I believe the answer is:
prologue
'introduction' is the definition.
(I know that prologue is a type of introduction)
'look into quiet villain's' is the wordplay.
'look' becomes 'lo' ('lo' is an archaic exclamation meaning 'look!').
'into' is an insertion indicator.
'quiet' becomes 'p' (music symbol for 'piano', ie soft or quiet).
'villain' becomes 'rogue' (rogue is a kind of villain).
'p'+'rogue'='progue'
'lo' going within 'progue' is 'PROLOGUE'.
(Other definitions for prologue that I've seen before include "Preface to a literary work" , "Foreword" , "Introductory scene" , "Start to play" , "Introductory piece" .)