Neverseen

You might be looking for Keeper of the Lost Cities Book Four: Neverseen.

The Neverseen is the name of one of the rebel groups in the Lost Cities. They oppose the rule of the Council, and they have wreaked havoc on the Lost Cities to make their presence known to everyone.

Origin
For thousands of years, the Council reigned supreme. They were the wisest, most talented members of the elvin society, working together for the greater good. But in the past few decades, humans had developed weapons powerful enough to destroy the planet. Therefore, about sixty years ago, a measure was brought before the Council to create a new Sanctuary specifically for humans, to relocate them for the good of the earth—and their own safety. It had a lot of support. Some very influential people had grown tired of hiding in the shadows while humans run amok throughout the globe. But the Council rejected it, refusing to imprison an intelligent species.

The supporters of the initiative were angry with the Council. Some called for members to resign. There were threats to go ahead with the plan. The Council did not regard the threats. The human's thoughts were suddenly turned to initiating with a war against elves, because, not known by the councillors and the public at the time, the Neverseen had been kidnapping humans for experimentation. The councilors decided the humans had turned on the elves, and forbade any human contact, not knowing the human's had a perfectly logical reason to attack.They recruited Telepaths to keep their minds open for any suspicious activity going around in human thoughts. All talk of rebellion vanished, and the Council was satisfied.

However, the supporters of the initiative moved underground, and some of the more aggressive ones formed the rebel group now known as the Neverseen. The others formed the Black Swan.

Mark of the Neverseen
The Neverseen wear a patch on their cloaks and an armband underneath, both with their symbol on it. The symbol is a white circle with a white eye in the center. This symbol has been in some of Sophie's nightmares.

Known Rebels
"'But I won't be silenced! Because the old ways are failing—and have been failing for centuries. This world doesn't need diplomacy. It needs quick, decisive leadership from someone who offers actual solutions. Someone not afraid of making the hard choices. Someone willing to make changes.'"Fintan Pyren is the leader of the Neverseen and a powerful Pyrokinetic. He knows how to spark Everblaze and he was the first Pyrokinetic to be able to do so. He was a former member of the Council before the discrimination he faced because of his ability drove him away from his noble duties and led him to become a rebel. Brant was the Pyrokinetic who burned Sophie and set the fire that had killed Jolie. He was trained by Fintan to spark Everblaze. In Lodestar, his skull was crushed into gray matter by a falling huge chunk of the ceiling after he was shoved by Mr. Forkle, in the crumbling remnants of Lumenaria. Gisela is a polyglot and one of the many Neverseen members who tried to kidnap Silveny. Keefe Sencen had thrown a goblin throwing star at her, giving her a scar at the end of Book 2. She is the one who developed the Lodestar Initiative and was one of the leaders of the Neverseen until Fintan captures her into an ogre prison and tortured her using ogre methods, throwing her off the leadership podium and rearranging the hierarchy of the Neverseen. As of Lodestar, she has escaped from the prison, and she demands Keefe not to be affiliated with the Neverseen even though she was the one who dragged him into the organization in the first place. She is believed to have killed Cyrah Endal but it is unclear whether that is the truth. Ruy is a Psionipath who attended Exillium. He was recruited by Gethen. He had been banished since he was young, the reason being "proven unstable and unfit for society".  Alvar is revealed to be part of the Neverseen at the end of Book 4. He was one of the youngest to enlist, and he is also the one who had spied on Sophie when she was just five and still in the Forbidden Cities. But in Nightfall he was found in Lady Gisela's nightfall bound and beaten and was sedated with a powerful drug called soporidine. Alden, Fitz, Keefe, and Sophie went to his cell with the antidote to wake him up upon which Alvar was in a frantic state and finished the book with one of Shannon Messenger's famous cliffhangers saying "Who's Alvar?" Keefe joins at the end of Neverseen, and in Lodestar, it was revealed that he joined as a double agent and is trying to gain intel to destroy the Neverseen. Keefe leaves the Neverseen again at the end of Lodestar. Gethen a telepath and is also the mysterious jogger who tried to capture Sophie in Book 1 He was later one of her kidnappers at the end of the book. The Black Swan eventually captured him. He was traded away to the Council and was imprisoned in Lumenaria until he, Fintan, Brant, Ruy, and the anonymous prisoner (Vespera) used their mental energy to break down the walls of Lumenaria so that they could wreak havoc and escape at the same time. Trix is a Guster and keeps himself concealed with the Neverseen cloak. In Lodestar, he is one of Wylie Endal's abductors. Umber is a Shade and keeps her appearance concealed with the Neverseen cloak. She is described to be a more powerful Shade than Tam Song. She is one of Wylie Endal's abductors. Jolie was a double agent for the Black Swan, gathering information about the Neverseen for them. She was discovered and was killed in a fire that Neverseen member Brant set. However, she had left records of such information and hid it away, waiting for the Black Swan to find it. Vespera is an Empath and is an ancient. She is the founder of Nightfall. She was rescued from Lumenaria in Lodestar.
 * Fintan Pyren
 * Brant 
 * Gisela Sencen
 * Ruy Ignis
 * Dwarves
 * Alvar Vacker
 * Keefe Sencen (temporarily)
 * Gethen
 * Trix
 * Umber
 * Jolie Ruewen (Temporarily)
 * Vespera