Menace afterwards includes right mess (8)
I believe the answer is:
threaten
'menace' is the definition.
(I know that menace can be written as threaten)
'afterwards includes right mess' is the wordplay.
'afterwards' becomes 'then' (I've seen this before).
'includes' indicates putting letters inside.
'right' becomes 'r' (common abbreviation).
'mess' becomes 'eat' (mess can mean to eat).
'r'+'eat'='reat'
'then' going around 'reat' is 'THREATEN'.
(Other definitions for threaten that I've seen before include "Put at risk, endanger" , "indicate danger" , "Be menacing" , "Menace - impend" , "Utter menaces" .)