clue

• 茫无头绪

  make neither head nor tail of it

• 找出头绪

  discover clues

• 整理出头绪

  straighten things out

• 事情有了些头绪。

  Things have become clearer.

• 三天来他们没有侦察到一点头绪。

  After three days they hadn't discovered a single clue.