An arresting figure in many a musical work (3)
I believe the answer is:
cop
'an arresting figure' is the definition.
(I've seen this in another clue)
'many a musical work' is the wordplay.
'many' becomes 'c' (C is the Roman numeral for 100).
'a musical work' becomes 'op' (abbreviation for opus).
'c'+'op'='COP'
'in' is the link.
(Other definitions for cop that I've seen before include "Policeman (colloq.)" , "Policeman (slang)" , "Police officer (slang)" , "Policeman (informal)" , "Member of the police force and an arrest" .)