The Use of Spies/The Use of Intelligence focuses on the importance of developing good information sources, and specifies the five types of intelligence sources and how to best manage each of them.
Learning highlight : <<有乡间，有内间，有反间，有死间，有生间>> ~ There are local agents, inside agents, double agents, doomed agents and living agents.
Cache is well hidden away from plain slight; need to remove camo but do it with care ~ safety first !
Bonus' data to collect : what is the nearby house's number (single digit) ? Take it down as C13.
Bonus cache : GC49EWV (The Art of War Bonus - Right Flank).