Performance of beheading? (9)
I believe the answer is:
execution
I believe this clue is a double definition.
'performance' is the first definition.
(I know that performance can be written as execution)
'beheading?' is the second definition.
(beheading is a kind of execution)
'of' acts as a link.
(Other definitions for execution that I've seen before include "The carrying out of" , "Topping" , "style of musical performance" , "Eg, beheading" , "Queen of Hearts' order" .)