Answer:
There is an ancient invention. Still used in some parts of the world today. That allows people to see through walls.
I'm light as a feather, yet the strongest man can't hold me for more than 5 minutes.
My first is twice in apple but not once in tart. My second is in liver but not in heart. My third is in giant and also in ghost. Whole Iβm best when I am roast.
Above all things have I been placed Thus have I, a man disgraced. I describe sunlight or lock But after all, I'm just a rock
It holds most knowledge that has ever been said. But is not the brain, is not the head. To feathers and their masters, it's both bane and boonΒ One empty, and one full.
If you can get this professional's attention you can get where you need to go for a price.