therein

/ðɛrˈɪn/
adverb
  1. In that place, document, or thing.
    • She read the contract carefully, and therein she found a hidden clause.
    • The forest is vast, and therein live many rare animals.
    • The treasure was hidden in the cave, and therein lay the mystery.
  2. In that particular respect or detail.
    • The plan seemed perfect, but therein was the flaw.
    • He made a mistake, and therein lies the problem.
    • She trusted him completely, and therein was her error.