Who Knocked Out Sherlock?

After a chess game with Dr. Beaky, Sherlock finds himself knocked unconscious in the middle of an alley. The criminal is one of the inhabitants of the zoo who holds a grudge against Sherlock. The Hamsters? The White Zebu? The Okapi? Who could it be? In the meantime, Sherlock finds himself addicted to video games while he pretends it's not true. But Hermione is on to him!