So, in short, what happened?
Who and why?
[spoiler]All begins with Leolinus.
Having been thwarted by Roberto too many times, he felt revengeful, a sentiment encouraged by his demonic masters. He felt that, whatever he was doing, Roberto was always in his way. So he decided to remove the obstacle.[/spoiler]
How?
[spoiler]Leolinus is arrogant, but not stupid. He knew he couldn't face Roberto directly, as Flambeau magi are the masters of direct confrontation.
He thus tried to circumvent this, by studying his enemy's weaknesses. Be it through spies, rumors or demons, he learned about Roberto's True Love. And thus came his rough idea of a trap: Capture Soteira, and use her as a bait for Roberto.
Despite being senior to Roberto, he felt like he wasn't up to the task (I took him from novus mane, rebuild and advanced him like I do for NPCs: 30 xp/year). He wasn't powerful enough to capture the princess, he also had no way to kill Roberto one that was achieved, nor did he have allies that could do that.
So he made a lot of demonic bargains in order to gain the knowledge and power he lacked (virtue "mentored by demons", six times). It is through his tutors that he learned of Attumah, the sleeping devil of Herakleion.[/spoiler]
Attumah?
[spoiler]Yes. Through a string of intermediaries, Leolinus managed to buy enough items to survive underwater. He went to Attumah's forgotten prison and freed him. The beast almost killed him there and then, but Leolinus was able to convince him and strike up a deal. Attumah alone would never be able to gain the throne of Herakleion. Leolinus could give it to him... But sooner or later, Roberto would come rescue his beloved, and Atumah would have to face him. Leolinus offered his help in all of this, explaining that Roberto was his enemy too.[/spoiler]
The spell
[spoiler]Back on solid ground, Leolinus called upon his allies, spending many seasons to create his masterpiece: A ritual that would roughly duplicate "Aura of Rightful Authority", but over a whole city (boundary + 2 size), enabling him to make anyone the people's natural leader.
Of course, he didn't reveal to Attumah that this would only last one year. Not that this would change much one the beast had secured his hold on the city, though.
Once ready, he conferred with attumah, and planned carefully. Leolinus cast his Ritual, making the entire city loyal enough to Attumah to allow him to enter the city with a small force, steal King Triton's trident, and attack him by surprise, far from his guards. With the king dead, the only "legitime ruler" left was Attumah, who had no trouble bringing the city to heel, and capturing Soteira.
As the spell only encompassed the city, those outside escaped its effect, but Leolinus was arrogant enough to discard them as negligible rabble[/spoiler]
What's the deal with Soteira?
[spoiler]Leolinus is crafty and cautious, and doesn't underestimate Roberto.
His first plan called to just lead Roberto into a huge trap and kill him.
But he thought maybe that would fail. Maybe Roberto would escape, maybe he would manage something to beat up the odds, whatever.
So he needed a backup plan. And what's better than having your enemy killed by the one he loves? He thus enslaved Soteira through Mentem magics: She was to be sent to the dungeons, act as normal, but, once alone with Roberto, to try to kill him at all costs when he was most vulnerable. This failed miserably, because, whatever his strengths and intelligence, Leolinus was oblivious to the power of True Love.[/spoiler]
Riad and the messengers
[spoiler]Once the city secured, the next stage was in luring Roberto. He needed to ensure at least some of the messengers would reach Roberto, without the Flambeau being able to suspect something. So, using flunkies with mentem magics was out: This needed to be as genuine as possible, with someone truthfully asking for Roberto's help
Leolinus simply created enough false memories in enough villagers to ensure they'd do something.[/spoiler]
What's the deal with Riad's adventures?
[spoiler]He had spend years learning about faeries, both to know how about herakleion and the merfolk, but also to find allies against Roberto. He had struck deals with some of these: They would help one of the townspeople reach Roberto, by giving him a grand adventure that would, in turn, strengthen them, especially as word of their existence reached the Order of Hermes.
This is why Riad lived all sort of "Arabian nights" adventures, in a separate story call "the quest for the fire wizard"[/spoiler]
What's the deal with the big storm?
[spoiler]That was me shoehorning one of those story flaws that never come into play ^^
Since the magi were using Johan VanHalen, I figured that the sea hag had found him, and was waiting in the sea for the first opportunity to strike at him.
So, once she could, she basically expanded a lot of might in order to make his life miserable and frighten him. At worst, he'd have lost his ship but she'd have carried him to safety on some remote island. That's also why the return was peaceful: A trick, once done, ain't usually repeated.[/spoiler]
What happened with Nera, thula and the ambassadors?
[spoiler]I originally planned for Leolinus to have also enslaved all the villagers in Riad's absence, with them trying to poison the magi. I just forgot it, so everything was fine on that front.
Leolinus and attumah expected Roberto's arrival. They had rotating teams for flunkies ready to answer the call, and lead the magi into a big, big ambush in which they'd have been skewered.
But remember that arrogance I spoke about before? The same merfolk Leolinus had discarded as Rabble heard the call, and their intervention foiled his main plan, allowing the magi to avoid the ambush and lead attumah and his forces on a merry goose chase.[/spoiler]
Soteira, in the dungeons
[spoiler]That's Leolinus backup plan: Should Roberto somehow enter the city, have the princess in the dungeons, and watch for them. Hopefully, the magi would be trapped there and be easily killed. And at worst, this would help sell Roberto the message that he could trust the bewitched Soteira, ensuring his eventual demise at her hand. But that was Leolinus second big mistake.[/spoiler]
Where was leolinus the whole time? Leolinus in the dungeons?
[spoiler]As said just above, Leolinus wanted to watch the dungeons for Roberto, but was fearful enough of the magus to avoid him at all costs.
So he used an Intangible tunnel to Soteira's spell, seeing and hearing through InIm spells, and projecting his image through CrIm.
He was, otherwise, holed up in the palace. He hoped to be able to secure an arcane connection to Roberto, but failed.
When Roberto confronted attumah, it was he that cast spells on Roberto, using the crowd's roar to hide his incantations. He tried the call to slumber, hoping to provoke a momentary slip on Roberto's part, but didn't manage to pierce his parma[/spoiler]
What's the deal with Soteira?
[spoiler]She was a faerie princess. She had now assumed a new role, that of the queen, with the might that goes with it. This is further reinforced by her crown and trident.
She had 2 reasons to want to marry Roberto: Love, and her people customs (in ars meta faerie terms: it makes for more stories, and thus vitality).[/spoiler]
I believed I've covered everything, if you have more questions, feel free to ask them!
(My post was almost eaten, but, luckily, I had been paranoid and copied it before. relief!!!)
. Then his gold ruby ring. Always that. A silver crucifix. A rosary worn around his wrist under his glove. Black eel skin gloves. His satchel with whatever trinkets he has in that stupid man-purse of his. 
I can see it now 