Plot to murder princes about nothing (8)
I believe the answer is:
conspire
'plot' is the definition.
(conspiring is a kind of plotting)
'to murder princes about nothing' is the wordplay.
'to murder' is an anagram indicator (the original order of letters is destroyed).
'about' indicates putting letters inside.
'nothing' becomes 'o' (looks like zero - 0).
'princes' is an anagram of 'cnspire'.
'cnspire' going around 'o' is 'CONSPIRE'.
(Other definitions for conspire that I've seen before include "Collude" , "scheme" , "Plot secretly" , "'Plot, connive (8)'" , "implicated in plot" .)