Caught!
The President explains Shinra Corporation's interest in the Ancients, or Cetra. He states that he believes Aeris is the key to the promised land, a land full of Mako Energy. This creates yet another places for Shinra to destroy with its life - sucking Mako Reactor. After the meeting, AVALANCHE is taken to the holding cells on the 67th floor.
While in the cell, approach the door so you can speak to the other characters. When you're finished, take a nap. When you awake from your sleep, you'll notice your cell door is wide open. What the...?
Inspect the downed guard and then wake up Tifa. After getting the cell key from the downed guard, Cloud frees the rest of the team. But something's seriously wrong here: All the lab technicians are dead and Jenova is nowhere to be found. To find out what in the world is going on, follow the blood trail to the President's office.
This leads you to the site of President Shinra's body slumped over his desk. It looks like Sephiroth is the culprit, but he's nowhere to be found. Soon Rufus, President Shinra's son, lands his helicopter on the roof. Take this opportunity to meet the new leader of Shinra Inc. Cloud will send away the rest of the party when this occurs.
When Tifa leaves, redistribute your Materia. Give Aeris the "Lightning" and "Restore" Materias and make sure Red XIII has at least one Spell Materia.
As soon as you're finished, head for the elevators. As soon as Barret, Aeris, and Red XIII enter the elevator, they get ambushed by Shinra security.
Boss Fight: Hundred Gunner and Heli Gunner
The team must fight at long-range against an enemy specially equipped for just such a fight. Barret is the only character who can damage the bosses with his normal attack. Everyone else must use magic or Limit Break attacks. The Hundred Gunner is especially weak against Lightning, so cast the Bolt spell as much as possible. After substantially damaging the boss, it transforms and begins charging its super weapon.
Note:
It takes the boss two turns to prepare its cannon, which should give you plenty of time to finish it without taking a hit.
When the Hundred Gunner gets destroyed, a Heli Gunner descends upon the party. This battle is similar to the previous battle. Focus on long-range attacks, Bolt spells, and Limit Breaks. Also, keep a close eye on your HP.
As the Heli Gunner nears death, it transforms and begins unleashing stronger attacks. Keep up your pace and the fight should be over quickly. For defeating both bosses, you're rewarded with a Mythril Armlet.
After the boss fight, the scene switches back to Cloud and Rufus. You're giving a chance to equip Cloud, which you should accept. Give him a Restore Materia and spell Materia combined with the "All" Materia. You may also want to place the "Elemental Bolt" Materia combination in his armor. The battle begins whenever you're ready.
Boss Fight: Rufus and Dark Nation
Your first order of business is getting rid of Dark Nation. Its Bolt attacks are powerful and it casts lots of protection spells on itself and Rufus, which tends to make the fight tougher than it has to be.
If you equipped Cloud with the "Elemental-Lightning" Materia combination, you won't need to worry about Dark Nation's attacks. Rufus isn't a tough opponent either. Keep your HPs up and use your Limit Breaks when they become available. When Rufus can't take any more, he grabs his chopper and flies away - like father, like son. Survive this battle and you'll receive a Protect Vest and a Guard Sourse.
With Rufus out of the way, find Tifa and then join the rest of the party in the lobby.