Machiavellian line penned by children’s author (7)
I believe the answer is:
plotter
'machiavellian' is the definition.
(thesaurus)
'line penned by children's author' is the wordplay.
I cannot quite see how this works, but
'line' could be 'l' (used when specifying particular lines from a poem) and 'l' is present in the answer.
'author' could be 'potter' (Beatrix Potter 1866-1943) and 'potter' is present in the remaining letters.
This accounts for all the letters.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for plotter that I've seen before include "Schemer" , "Conspirator's" , "Conspirator" , "One who schemes" .)