神不知鬼不觉
shén​bù​zhī​guǐ​bù​jué

top secret

  1. 神 shén noun
    god
    god; deity; divinity; a supernatural being like a spirit or immortal in religion or mythology
  2. 不知 bù​zhī adverb
    unknowingly
    without realizing; unconsciously; in a way that one is not aware of
  3. 鬼 guǐ noun
    ghost
    ghost; disembodied spirit; devil
  4. 不觉 不覺 bù​jué adverb
    unconsciously
    Without one's knowing; unconsciously; in spite of oneself.