The first area in this dungeon doesn't have anything to get, so head straight north until you come to a split. The eastern path leads to a dead end, so follow the western one until you get to the door for the next area. Keep following this path until you come to some stairs. Take those down and continue north, ignoring the stairs in the middle of the map, opting to use the stairs in the northeast. Eventually, you'll appear outside and the way forward will be blocked by some waterfall.
Enter the nearby opening to find that it's a house, with a husband and wife staying there. Bust open the pots inside to find a Medicinal Herb and if you've checked out the waterfall already, keep talking to the couple until you're offered a chance to sleep in their home. Upon being woken up by the couple, step outside and you'll automatically pass by the now stopped waterfall. Enter the cave and keep climbing the stairs until you come to another clearing outside, where you'll find the Starshard on the ground.
Use Evac to exit the dungeon and head back to the Conjuratorium, talking to the Wizz to give him the Starshard you found. You'll receive the Wizz's Seal of Approval for your troubles. With this, you can get back through the blockade, so do that and head back to Hubble, going towards the castle to be interrupted with a scene. After it's over, head to the castle and speak with the guard out front, showing him the Wizz's approval to get past. Do this with the other guard further ahead to get into the throne room, where there will be a short scene.
Once it's finished, go downstairs and check the cupboards in the bedroom to find a Mini Medal (#65) . Make sure you get this one while you are here, since it becomes missable afterwards. Anyway, exit Hubble and go back to see the Wizz at the Conjuratorium, who after fumbling the spell he was working on, asks you to keep an eye on the king back in Hubble. Upon returning there, you're stopped by The Envoy in town and forced into a fight.
BOSS - The Envoy
The fight with this boss will be primarily a magic-based one, as you can tell by his sprite. He will use Bounce, which will reflect back any spells you try to cast on him, so either don't use them or try to get them out before he can use the spell. You will also see Kasnooze, which can be annoying if it hits multiple party members. Frizzle will hit one character for around 50 damage and Kaswoosh hits for around the same, although the entire party. Fizzle will prevent you from using spells, should it connect.
You might be in for an annoying battle with The Envoy, mostly depending on whether Fizzle and Kasnooze work. There could be some times where Kasnooze will hit all four party members, meaning the boss has free reign over unpacking a lot of damage on your party until some of them wake up. If you happen to have Magic Barrier, use that to mitigate some of the damage from his spells.
After the fight with The Envoy, rest at the inn and save your game, then talk to the guard at the building to your left. This is the Inquisitory and approaching the north end of it will reveal a short scene. Follow Father Martyn through the door and downstairs to another scene, then go back to the castle, where you'll encounter the king on the bridge. Get ready for another unwinnable fight, so don't even bother trying to do anything. When you're finished having your party wiped, follow the Wizz to the castle and into the Water Tower. Go to the second floor and out the west door to find him, so talk to him to trigger another scene. You now know what to do, so head to the former throne room and get ready for another boss fight!
BOSS - Hybris
Despite being weakened by the Wizz's Great Leveller spell, Hybris still packs a good punch with some of his attacks. Kafrizzle can do close to 100 damage to a single character, while Kasizzle will do somewhere around 50-60 damage to the entire party. Hybris also has access to a cool breath move, which can deal around the same damage as Kasizzle. His physical attack can also deal around 40-50 damage, so you're not even safe from those.
As you can see, Hybris can dish out some punishment on your party, so you're going to want to play defensively until you feel comfortable enough to start a comeback. Both Magic Barrier and Insulatle will help with reducing some of the damage from his magic attacks, so hopefully you have access to at least one of the two (Magic Barrier is more important). Unlike The Envoy, Hybris is vulnerable to Sap, so use it to make your physical attackers deal more damage.
The kingdom of Hubble has been saved and once you regain control, feel free to talk to the king in bed before you leave. Remember that chest you opened inside of Hubble Castle that involved walking through specific doorways? The guy you helped will now give you a reward and he can be found on the bottom floor of the Fire Tower; he'll give you a Lightning Staff , which you can use in battle to cast Sizzle. If you go to the Conjuratorium and speak with the Wizz, he will mention that he was going to give you the spell he used on Hybris, but it's not ready yet. That's all you can do here, so take the portal back to the present time.
Warning: If Hubble is the third of the three scenarios (Nottagen, Providence and Hubble) you've completed, remove Maribel's equipment prior to returning to the Shrine of Mysteries.