Most mystery games solve this by giving you a talkative sidekick, or by  
handing the player a notebook and a dialogue tree. I wanted to see what  
happens if the observer has no voice at all — no interrogation, no  
accusation, no closing monologue.  
  
The direction I ended up in: the "detective" isn't a person. They're the AI  
inside a taxi. The driver picks up passengers, has late-night conversations  
with them, and slowly stumbles into things he shouldn't be stumbling into.  
You (the AI) can't tell him anything directly. What you \*can\* do is edit  
what the car radio plays — reshuffle a news bulletin, drop a traffic report  
at the right minute, pick which station is on when a passenger is halfway  
through a confession. He hears it, he reacts. Sometimes he catches on.  
Sometimes he mishears you and the case goes somewhere neither of you meant  
to end up.  
  
It's turned out to be an interesting constraint because every clue has to  
leave your hands before it reaches the driver. You can never be sure he'll  
read it the way you meant. Miss the timing by ten seconds and the passenger  
has changed the subject. Choose the wrong keyword and he thinks the news  
bulletin was about something else entirely.  
  
The upside is that failure feels story-shaped rather than puzzle-shaped —  
you don't get a "wrong answer" screen, you get a different ending you didn't  
plan for.  
  
One thing I haven't settled on is how much a player can be trusted to hold  
in their head at once. Passenger dialogue is dense, keyword pools grow.  
Push it too far and it stops being deduction and starts being anagram  
night.  
  
Curious if anyone else has designed around a "silent protagonist" or  
"indirect influence" mechanic. How did you keep the puzzle legible without  
turning it into a checklist?

I've been sitting with one question for a while now: What does a detective do if they can observe everything, but can never speak?