After the forst part is done collect two potions off one of the guards. Find Biggs, Jessie and Wege and input your name, Then, do the same for Barrett. Run through the alley and onto a T-shaped bridge. Take the first left and run down into the main Reactor. Barrett will say something then join you. Go and talk to Biggs to open the door and then talk to jessie to open the other one.  Run through the door and run right. Collect the Phoenix down from the chest and go talk to Jessie, she will open the lift. Press a button in the lift and go down to the bottom floor. Run down all the stairs, basically just following Jessie. Collect the potion that is in front of jessie when she stops. Go down the ladder and then go down the next ladder. You'll be at a Save point. Run across the bridge and pick up the Restore Materia.

Boss: Guard Scorpion

Make cloud use Bolt magic and Barrett use attack. It would be wise not attack when it's tail goes up or you might risk losing a lot of health or maybe even game over on rare occasions.