undercover
un-der-cov-er
adverb
Operating or working secretly, often to investigate or gather intelligence.
"The detective went undercover."
adjective
Done or working secretly, especially for intelligence gathering or law enforcement.
"She was an undercover journalist."
Thesaurus
Synonyms: surreptitious, hugger-mugger, secret, clandestine, hush-hush, cloak-and-dagger, covert, hole-and-corner, underground