You'll start this Chapter by getting a new party member -- Shade! She's a mandatory party member for this next section, so choose the rest of your party, then head left to find a Chao Egg. Go back down the hill on the left and Fly southwest. Jump to the round platform, then Jump again into the hole. Interact with the first generator, then leave. Now that Eggman's lab's electricity is flowing once more, head to the upper room of the eastern building. Save your game, then go through the door east of the ramp. This is the Hazard Vault, and you'll be fighting a boss here!