Young wizard’s handling spell, ultimately intriguing people (8)
I believe the answer is:
plotters
'intriguing people' is the definition.
'young wizard's handling spell ultimately' is the wordplay.
'young wizard's' becomes 'potters' (Harry Potter).
'handling' means one lot of letters goes inside another.
'ultimately' says to take the final letters.
The final letter of 'spell' is 'l'.
'potters' enclosing 'l' is 'PLOTTERS'.
(Other definitions for plotters that I've seen before include "People planning" , "eg, Guy Fawkes and co" .)