plainclothes russian

• операти́вник

  detective, criminal investigator, operative, plainclothes officer

• шпик

  salted pork fat, bacon fat, lard (in slices)

  sleuth, plainclothes detective, police spy, informer

Examples

• За домом следил незнакомый шпик.

  An unfamiliar plainclothes police officer was watching the house.