undercover

卧底的、乔装的

An undercover officer spent two years inside the gang.

一名卧底警员在帮派里待了两年。

秘密的、暗中进行的

The police launched an undercover investigation into the bribes.

警方针对这些贿款展开秘密调查。

卧底、秘密地

She went undercover to expose the illegal dumping.

她乔装卧底，揭露非法弃置废弃物的行为。