“I told you: their castle is too heavily warded, and full of magical traps that would trip up even Helion.
Rhys is having Helion teach him about truly impenetrable shields
Helion, High Lord of the Day Court and Rhys’s closest ally, had been the most involved. / But the male had one thousand libraries at his disposal, and had put them all to good use for the treaty. “
Feyre turned to Rhys. “We need to ask Helion to visit.
Books tumbled off the shelves in Helion's thousand libraries
"No, it's a Symphonia, a rare device from Helion's court."
"Helion?" Azriel asked, eyes pained. "I told him before he left yesterday. Pulled him aside when Feyre had winnowed home, and begged him on my knees to find something in his thousand libraries to save her. He said every head librarian and researcher who can be spared will be put on it."
"Because we need his libraries."
Cassian had heard the rumors of Helion's rare pegasuses.
"Perhaps an ancestor of mine once used it, and the warning of its cost is imprinted upon my blood." (and we later find out that Theia once had the mask - Theia who has powers quite similar to Helion)
"Something bothering you at home?" Rhys inquired falling into step beside the High Lord.
Every mention of Helion in SF is a clue into Lucien's future. Just like the scene in Lion King where Mufasa is telling Simba how everything the light touches will be his one day, Sarah is showing us the same in Silver Flames through Lucien's own father. The things he'll have access too, potential problems he may deal with, what he will be able to do with his power (impenetrable shields just might come in handy when dealing with Koschei!), the way the NC looks to the Day Court for it's help, that fact that Helion seems to have his own connection to the would have been Dusk Court what with the pegasus and comments on how "maybe an ancestor of his" once used the mask especially when in mythology Theia is the mother of Helios, the fact that we know there are potential issues in the Day Court right now and there's no better POV to lead the reader there to learn of those issues than Lucien.
Perhaps Amren was working on some way to undo the bargain—if anyone could think of a way, it would be her. Or Helion, he supposed. Cassian and Azriel were beyond Rhys’s and Feyre’s daemati range, though. They’d have no news of anything.
Feyre winced. “Mor left for Vallahan this morning and is out of our daemati magic’s range. Az can’t go in alone. We need you, Cassian.”
Sarah repeated how when someone is on the continent, Rhys and Feyre are unable to contact them. When SF ended like this: "I hope that whatever Morrigan is doing in Vallahan will counteract the damage my father will unleash" it does make me wonder if the next book will start with Mor not returning when she was supposed to and Feysand sending Lucien to the continent to track her down
What role Vallahan's hot-tempered king and proud people would play in this new world of theirs was yet to be decided, though much of its fate seemed to depend upon Mor's now-frequent presence at their court as Rhys's emissary."
"I've spent weeks in that blasted court," Mor said, poking at the flaky pastry beside her teacup, "freezing my ass off, trying to kiss their cold asses, and their king and queen refused the treaty.
"Why won't they sign it?"
"Because those stupid human queens are stirring - their army still isn't disbanded. The Queen of Vallahan even asked me what the point of a peace treaty would be when another war, this time against the humans, might redraw the territory lines far below the wall. I don't think Vallahan is interested in peace. Or allying with us."
"So you're supposed to convince Vallahan not to start another war, and I'm supposed to convince the human queens not to do so, either?"
"You won't get near the human queens," Mor said frankly. "But from what I observed in Vallahan, I know they're up to something. Planning something. We just can't figure out what, or why the humans would be stupid enough to start a war they cannot win."
"There's one person who knows those queens inside and out. Who can offer some insight." / "Vassa." Cassian hadn't dealt much with the ousted human queen - the only good one out of the surviving group, who had been betrayed by her fellow queens when they'd sold her to a sorcerer-lord who'd cursed her to be a firebird by day, woman by night."
Mor has been unable to get Vallahan to sign the peace treaty as they are weighing the possibility of starting another war against the humans to gain more territory. They know the remaining human queens have been stirring (queens plural), that their army is not disbanded and the IC knows that Vassa is their best contact for information regarding the queens, Vassa who Koschei is about to call back.
I think it's incredible when readers claim Lucien is irrelevant to the plot, that Sarah forgot about him. Right now the current plot / current threats in ACOTAR are 90% connected to Lucien when you consider how the political drama going on in their world is focused on Spring (with Beron setting his sights on potentially taking over the land in that court due to it's weakened state), with the fae in Vahallan setting their sights on the human lands and the remaining human queens keeping their army in reserve, with Vassa being the main link to all of that and Vassa being the main connection to Koschei.
Spring? The human lands? Name a single other potential leading character who has a stronger connection to both.
Lucien who helped the humans sort out their politics after the war.
Lucien who is now permanently stationed in Spring and only gives reports to Feysand in private.
Lucien who has been to the continent and Koschei's lake.
Lucien who is friends with Vassa.
Lucien who Sarah wrote as setting his sights on his target (Koschei).
I know Elain will be the one to save the day as all SJM fmc's do but she typically writes the mmc as being the gateway to that. Feyre would not have been involved in the war with Hybern had Rhys not been the one to draw her in, Rowan was Aelin's "in" with Maeve and all that came from that, Yrene would have never taken up the battle with Erawan had Chaol not landed on her doorstop and Nesta would not have trained had Cassian not continued to push her.
Elain will be the one to save the day in her story but it will be Lucien who will be the catalyst for her journey to begin.