Conspirator left trapped by Voldemort’s enemy (7)
I believe the answer is:
plotter
'conspirator' is the definition.
(I know that conspirator can be written as plotter)
'left trapped by voldemort's enemy' is the wordplay.
'left' becomes 'l' (common abbreviation).
'trapped by' means one lot of letters goes inside another.
'voldemort's enemy' becomes 'Potter' (Harry Potter in JK Rowling's books).
'l' inserted into 'potter' is 'PLOTTER'.
(Other definitions for plotter that I've seen before include "Conspirator's" , "Conspirator" , "Schemer" , "One who schemes" .)