On September 18, 1931, Shenyang fell into a sea of fire. When Lin Mo, a translator in the Northeast Army, witnessed the Japanese army slaughtering his colleagues, a gold pen of unknown origin suddenly slipped from his trouser pocket and fell into a pool of blood. When the Japanese Major leaned over to pick it up, Lin Mo tore off the fragments of the code book from the belt around his waist. At 2:17 in the morning, while fleeing, he ran into the backyard of a Chinese medicine shop. The shopkeeper scratched three times behind his ears with his little finger - this was the underground party's contact code.
