As mentioned on the previous page, there is a boss battle coming up that you should take some time to prepare for as it follows directly after an upcoming cutscene.
If you took the time to defeat the first Demon Wall, you may have employed the strategy of speeding up the Battle Speed to increase the amount of damage that your party could do during the course of that battle. Make sure that you drop the Battle Speed down to a slower pace before this next fight if required (though it is always best to keep it at high if you can).
Reminder that in the Zodiac Age version of the game you now have access to a Second Job Board for each of your characters. Check out the Jobs Section and make sure that you plan out your jobs accordingly.
Make sure that you cast 
Protect and Shell on each of your party members and set up a Gambit to have one of your characters cast 
Slow and/or 
Sleep on enemy combatants. Set up a few Gambits that utilize 
Potions or Hi-Potions to heal as the boss has large bursts of damage that could KO a party member before Cure or Cura has time to finish casting.
Walk towards the exit on the east side of the Valley of the Dead to initiate the cutscene. The whole party will be spotted and captured by Imperial Soldiers and Judge Ghis. They will turn over the Dawn Shard / Deifacted Nethicite to Judge Ghis after finding out that Vossler is in league with the Imperials.
Judge Ghis will send Ashe, Basch, Balthier, Fran, Vaan and Penelo to be taken to The Shiva and he will begin trying to assess the power of the stone within his ship. Once this happens, Fran will have a bit of a meltdown and will go into a rage. She will single handedly take out many of the surrounding guards.
Note that this effect actually carries over into the upcoming fight. Fran will be in a Berserker mode if you choose to use her in your party and her attacks are quite strong.
Level: 20
HP: 9,318
Steal: Potions (55%), Hi-Potions (10%), 
Black Belt (3%)
Vossler and four Imperial Soldiers will charge at the party as they attempt to make their escape. As mentioned above, Fran will continue in her Berserker mode and can be quite powerful if you choose to use her in your party at this point.
Start off by taking out all four of the supporting guards. They go down quite quickly and you do not want them getting in the way once Vossler gets low on HP.
Vossler will begin using Enrage once his HP drops below 40% and he will start dealing very heavy damage to his target. If Basch is in your party, Vossler will continue to target Basch until he is KO’d, but if not, he will target random party members as the fight progresses.
Using an Esper, such as your newly acquired Belias Esper, or Quickenings, can help end the fight much more quickly. You can also use Slow and Sleep on Vossler to limit some of the damage he does.
A video of the battle in the Zodiac Age version is included below:
Basch and Vossler will have one last conversation after the battle and before the team flees the imploding ship. The Dreadnought Leviathan and the Shiva will both be destroyed in the explosion.
This cutscene in the last section is the end of this chapter of the story. After the explosion and a few more scenes of dialogue, the game will transition back to Marquis Halim Ondore IV as he describes the next chapter of the story – Chapter 16: Biding Time (Section 3).
There are a few more cutscenes and then the story continues in the Royal City of Rabanastre in the Muthru Bazaar.
The Mist Seethes
The Mist Seethes Trophy is automatically obtained after you have completed the events on board the Shiva airship.
