Speak with the rest of your allies, then form two teams of four. Sonic and Knuckles must be on one team, and Tails and Eggman must be on the other. Whenever you need to heal your party, return to this room. For the next bit of the walkthrough, we'll refer to these teams as Team Sonic and Team Tails. Leave the stronghold now and enter the hallway. Defeat the Assault Drone and Seeker Drone out here, then take the Chao Egg at the end of the corridor. Now take the stairs up to Metropolis proper. Go down the adjoining hallway, then go left into the room there to find the Weapon Part 1.