Once you're ready, enter the room north of the steps taking you down to B1F. Head north through the room and enter the teleportation pad at the end. You're in room with Zinzolin and one of his Grunts. Move up and he'll notice you. After talking for a while, Hugh will finally arrive.
The two of you will team up against Zinzolin and the Grunt. Hugh will have the same party as before when you participated in the other Double Battle. The battle is on!
Double Battle: Team Plasma Zinzolin and Team Plasma Grunt
You will talk with Zinzolin. Eventually two Shadow Triad members will appear and you'll black out. Next, there'll be a cutscene where the Plasma Frigate flies into the air and sails away. You'll awake back on the Route 21 beach. Cheren will appear. Now it's time to head to Route 22!
Fly back to Humilau City and heal your Pokemon at the Pokemon Center. Once your Pokemon are healed, head onto Route 22 ! It can be confusing getting there, so we'll direct you.
Head north-east past the Gym and head over the bridge to your north. When you reach the path leading west, take it and move down the ramp to the shallows below. Move north-west under the walkway then continue north. Move west under the next one and head up the ramp. Continue west down the ramp onto the beach.
Guess what? You're in Route 22! From there, make your way west and enter the cave at the far end, which leads into the Giant Chasm . If you came here earlier, some Team Plasma members were blocking the road. But now that the Plasma Frigate has left Seaside Cave, you will be able to progress further in.