I've seen the special manga, including the "Generic" chapter, in Chinese. You aren't missing anything especially worthwhile. If you want to know the plot, someone injected one of the class guinea pigs with something. Based on what happened, Haibara thinks a member of the Black Org must have done it. At the end of the school day, Haibara finds a note in her shoe locker from this Org member. I presume the note is threatening all the children in Teitan Elementary. She is upset, Conan comforts her, and he decides to review the security camera footage of the lockers. Small footprints and the fact that no one tall shows up on camera cause Conan to realize the culprit is a kid and thus the Org member is an APTX victim. Haibara tells Conan there was a guy who worked with her in one of her labs and he might be the culprit.
Despite knowing a Black Org member is out to get her, Haibara goes to school the next day, and gets so nervous that she falls ill and goes to the nurse's office. Conan goes looking for and, surprise, she isn't there. Conan searches for Haibara, but she isn't anywhere to be found and, for some reason I can't figure out, Conan decides to not look for her, assumes she is OK, and decides to catch the chibi Black Org guy instead. Conan heads to Teitan Elementary at night and sees someone pull in the schoolyard with a large van. Conan then catches a miniature emo child burying gas canisters in the school yard. Haibara appears out of nowhere randomly, confronts the Black Org member, and reveals his codename is Generic.
Haibara and Generic have a chat about the past, his motives, and why the heck he decided to take APTX and become small and such. During this conversation Generic gets upset to the point of crying and reveals the gas canisters contain memory erasing compound. Generic then decides he wants to gas Haibara and Conan and pulls a spare canister from his sleeve. The day is saved when Genta jumps out of hiding and slingshots the canister out of Generic's hand. It turns out the detective boys were lurking around and overheard the long discussion about the Black Org and Sherry's history with Generic! Oops. Anyway, the canister falls to the ground and douses Generic with his own gas which knocks him out. He then forgets his entire past with the Org, is adopted by a random family, and can now live a happy, fulfilling childhood that doesn't involve freaky science experiments and a depressing dresscode. And no one explains who drove the bloody van into the schoolyard. The end.