What hides between Shadow and Light?

[Kedjane]

"Between light and shadow, exists an entire world. That world is necessarily our own.

Get out. Now.

O."

The light and shadow part references "penumbra", which is the area between light and dark. I haven't got an example for what a penumbra is in real life though.
The second part I don't really get and I'm guessing it's a grammar confusion/poor translation.
From what I remember 'O' is Neil Oswald, the cheif chemist that replaced Troy Retonesque in 1991. I think he was the one who put up all the laser mines and that he's the first dead guy you find (and draw blood from).