undercover
adj. 秘密的，秘密从事的；从事间谍活动的
例句
Officers had tailed the gang during a major undercover operation.
警方在一次重大的秘密行动中跟踪过这个团伙。
《柯林斯英汉双解大词典》
Journalists informed police who planted an undercover detective to trap Smith.
记者们向警方提供了信息，警方安插了一名卧底侦探诱捕史密斯。
Swanson persuaded Hubley to work undercover to capture the killer.
斯旺森说服了赫布利秘密工作以捕获凶手。
