secret plan vs intrigue

secret plan and intrigue both are nouns.

Word	Noun	Adjective	Verb	Adverb
secret plan	Yes	No	No	No
intrigue	Yes	No	Yes	No

As nouns, intrigue is a hyponym of secret plan; that is, intrigue is a word with a more specific, narrower meaning than secret plan:

secret plan: a secret scheme to do something (especially something underhand or illegal)
intrigue: a crafty and involved plot to achieve your (usually sinister) ends

Other hyponyms of secret plan include counterplan, counterplot, machination, cabal, conspiracy.

secret plan (noun)	intrigue (noun)
a secret scheme to do something (especially something underhand or illegal)	a crafty and involved plot to achieve your (usually sinister) ends
	a clandestine love affair

secret plan (verb)	intrigue (verb)
	form intrigues (for) in an underhand manner
	cause to be interested or curious