Thank you! Recognizing that our audience consists of many players not used to adventure games, and who still wanted to play an Agatha Christie game, I began by trying to give players hints to puzzles in several different ways:
1. Hints buried in the dialogue and actions of characters for those who play the game as a story. (My way!)
2. Hints in the Notebook for those who like to play the game as an adventure game.
3. A really obvious way to keep them from wandering, and er point them in the right direction...?
Once I had the finger, I then decided to make the finger's mechanism a puzzle as well, so that the players had something to solve in Poirot's office. They can still use it, of course, even if they don't know its secret.