Plot against English historian (4)
I believe the answer is:
bede
'historian' is the definition.
(I have seen 'Ecclesiastical historian ' mean 'bede' so perhaps 'historian' could also mean 'bede')
'plot against english' is the wordplay.
'plot' becomes 'bed' (a plot of land).
'against' means one lot of letters go next to another.
'english' becomes 'E' (abbreviation).
'bed'+'e'='BEDE'
(Other definitions for bede that I've seen before include "Jarrow monk" , "Ancient English historian" , "Ecclesiastical historian" , "Northumbrian monk and historian, d. 735" , "Venerable scholar" .)