Set spies to protect English dynasty (12)

I believe the answer is:

plantagenets

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'dynasty' is the definition.
I know nothing about this answer so I can't judge whether it can be defined by this definition.

'set spies to protect english' is the wordplay.
'set' becomes 'plant' (synonyms).
'spies' becomes 'agents' (secret agents).
'to protect' indicates putting letters inside.
'english' becomes 'e' (abbreviation).
'agents' going around 'e' is 'agenets'.
'plant'+'agenets'='PLANTAGENETS'

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