High-level plot for gore and mayhem (4,6)
I believe the answer is:
roof garden
'high-level plot' is the definition.
(plot of land at a high level)
'for gore and mayhem' is the wordplay.
'mayhem' indicates an anagram.
'for'+'gore'+'and'='forgoreand'
'forgoreand' with letters rearranged gives 'ROOF-GARDEN'.
(Other definitions for roof garden that I've seen before include "Elevated area of greenery" , "where domestic growth high?" , "where domestic growth is highest" , "that's grown at highest level" , "High-level greenery" .)