Huang Donglai and the others' escape from the Southern City Military Department went pretty much as planned, as mentioned in the previous letter, so there's no need to go over it again here.
Let's divide the story and start with Sun Yixie's side of things.
As you know, Brother Sun is "naturally the sixth brother," and he has an almost perverse talent for running away and hiding.
Don't be fooled by his habit of getting lost or buying train tickets for the wrong direction on a normal day; when it's time to flee for his life, he can instantly lock onto every exit in his vicinity, as well as all the nooks and crannies suitable for hiding.
This is much like how many people in their school days, upon entering a new classroom after being reassigned, would first observe and confirm how many attractive female/male classmates were present...
Except that Brother Sun has replaced the object of confirmation with escape routes and turned this behavior into an instinct.
