intrigue vs secret plan

intrigue and secret plan both are nouns.

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

As nouns, secret plan is a hypernym of intrigue; that is, secret plan is a word with a broader meaning than intrigue:

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

Other hypernyms of intrigue include game, plot.

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

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