Thank you for clarifying. I didn't know that about one-way mirrors.

Clue as in the board game, the Manhattan project was the name of the nuclear research that was done in Los Alamos during WWII, the Giver has the weird memory stuff, and the grimm reaper as in the person. Basically mystery, interesting but secretive science, capturing memories, and the one line about the people always dying and them waiting made me briefly think they were collecting souls or dead bodies. Not necessarily setting, but random aspects I got from the mood.
-Observing Anon