When he went back he couldnt find any traces of the girl and he is questionning everything atp.

Untill he overheard someone talking about “humans” who are near this forest, and some of then refuge in these trees during war or what not.

Deryn was sent to work by his mother because she is coerced by some high class people. The high class people might have safety or control over the umbral storm and poor people have to kill monsters so the world doesn’t get screwed over, and like prioritize their lives over everyone else or use the monsters as military weapons, antagonistic. The girl actually used to be part of them and decided that they are bad and became good, and got banished so she is hungry now.