Iron Flame by Rebecca Yarros

In the aftermath of an attack by the venin on the military outpost of Athebyne during the end-of-year War Games at Basgiath War College, Violet recovers from her injuries in Aretia, a town in Navarre’s Tyrrendor Province. Over the past three days, her world has been upended. Xaden Riorson, the third-year cadet she has fallen in love with, is part of a secret rebellion thought to have ended years ago. Some of Violet’s fellow students who survived Athebyne are also involved in the rebellion. Violet’s brother, Brennan, whom she believed had died six years ago fighting the rebels, is alive and the leader of the rebellion. The venin from her father’s folktales—dark magic wielders who draw power directly from the earth and control wyverns—are real and bent on destroying everyone on the continent. To protect the citizens within Navarre’s magic wards, which keep the venin out, the kingdom’s leadership has carefully hidden all of this and erased it from history.

Brennan and Xaden prefer to keep Violet in the dark about the rebellion’s details until she can master her magic to create a mental shield strong enough to block Dain Aetos, who can read memories. Violet distances herself from Xaden until he agrees to be fully honest with her. Andarna, one of Violet’s two bonded dragons, is taken to the Vale for the Dreamless Sleep, a critical process during which young dragons mature. Meanwhile, Violet, Xaden, and their peers are sent back to Basgiath for graduation. Colonel Aetos, who had sent them to die after Dain stole Violet’s memories, threatens their families’ lives if they reveal the existence of the venin. Dain tries, unsuccessfully, to reconcile with Violet, unaware of what really happened at Athebyne and the depth of his betrayal. Xaden graduates and is sent to Samara, a border outpost, while Violet and Xaden are allowed leave on alternate weekends for their dragons to satisfy their mating bond.

As her second year at Basgiath War College begins, Violet is excluded from participating in the rebels’ smuggling operation to provide alloy daggers to the gryphon fliers of Poromiel, a nation beyond the wards. Major Burton Varrish replaces Colonel Aetos as vice commandant of Basgiath and targets Violet, punishing her whenever Andarna fails to show up for flight maneuvers (they don't realzie that she is a child). On Conscription Day, Violet’s old friend, Prince Cam, crosses the parapet and joins her squad under the pseudonym Aaric Graycastle (his father the King, believes he is out enjoying life around the realm). As the year progresses, survivors of Athebyne begin dying one by one at the hands of Colonel Aetos’s assassins. Unable to lie to her friends, Violet distances herself from them to protect them, enlisting her scribe friend, Jesinia, to assist with her research into the First Six, the ancient beings who created the wards. Violet keeps this a secret from Xaden, who still refuses to share any information with her.

In the second-year Rider Survival Course (RSC), Violet and her friends are assigned to joint land navigation exercises alongside infantry, scribes, and healers. They fail the course when their bond to their dragons is severed by a signet-blocking elixir. Violet grows increasingly frustrated in class when venin attacks are hidden by their Battle Brief professor. Xaden learns of Violet’s research into the wards, and they argue about the one-sided trust he expects from her. As time goes on, Violet struggles to keep the truth from her sister Mira and best friend Rhiannon. She finally decides to tell Rhiannon about Dain’s signet and the fact that Athebyne survivors are being targeted for something they witnessed. Aaric reveals to Violet that he knows the truth about the venin and, unlike his father, King Tauri, wants to fight against them.

Eventually, Violet and her friends are seized for another RSC challenge—interrogation. Varrish attempts to extract information from Violet, even trying to use Dain’s signet on her, but fails. Jack Barlowe, whom Violet believes she killed with her lightning power the previous year, secretly returns to class after being healed. Violet learns that Xaden has been badly injured in a gryphon attack at Samara and deserts her post to visit him. Upon arriving at Samara, she finds Xaden completely healed and trusts her enough to bring her along to deliver smuggled daggers to the gryphon fliers. One of the fliers, Catriona “Cat” Cordella, is Xaden’s former girlfriend, which complicates matters. Xaden gifts Violet an alloy dagger to protect herself from the venin, but when she returns to campus, Varrish checks her person before she can hide it. Rhiannon teleports the dagger to her room with her signet, forcing Violet to reveal everything to Rhiannon and their other friends, Sawyer and Ridoc.

The group devises a plan to break into the sublevel vault of the Archives to steal the journals of the First Six. They manage to locate two of the journals—those of Warrick and Lyra. While Xaden takes Warrick’s journal, Nolon, the healer, catches Violet with Lyra’s journal and turns her in to Varrish, who tortures her for days. The only thing that helps her survive the ordeal is the vision of her dead friend, Liam Mairi, who encourages her not to break. Dain is brought in to read Violet’s memories, and after seeing the truth, he kills Varrish and helps Violet escape, just as Xaden arrives to rescue her. Violets mom sees her on her way out, reveals she didn't know that Violet was being tortured, and that everything she has done has been to help protect her children. She also briefly reveals that she and Xaden made a deal years ago, and his end of the bargin was to make sure Violet made it through school. After that chat, Xaden and Violet reveal the truth to all the students at Basgiath and offer any cadets who wish to desert the chance to return with them to Aretia. Violet and Xaden bring over 200 riders and dragons to Aretia, where Andarna awakens from the Dreamless Sleep. Mira soon arrives with even more riders after General Sorrengail, their mother, reveals the truth to everyone and gives them the choice to desert or stay. A rebellion has now started, a make shift war college is put into place so everyone can continue to train.

Felix, an Assembly member, teaches Violet to control her uncontrollable lightning power. Violet translates the warding ritual in Warrick’s journal, but her first attempt to raise Aretia’s wards fails. Against Xaden’s wishes, she travels with Mira and Brennan to Cordyn to persuade Viscount Tecarus, a potential ally to the rebels, to provide a luminary to power Aretia’s forges and make more alloy daggers. Upon arrival, Violet discovers that Cat is Tecarus’s niece and Xaden’s former betrothed. Violet uses her lightning to kill a venin in exchange for the luminary, but Tecarus demands they take 100 gryphon fliers to Aretia for training with the dragons.

For weeks, riders and fliers undergo training to build trust and teamwork. They also learn to weave Tyrrish runes, which store magic for later use. During a challenge to locate runes hidden in the Esben Mountains, Violet’s group is attacked by Varrish’s dragon, Solas. One rider is killed, but Andarna kills Solas to protect the group (which is a bad thing against the dragons). Cat and Violet eventually put aside their differences and form a tenuous alliance.

Violet continues to retranslate Warrick’s journal, with Dain’s help. He corrects her mistakes, leading them to a new way to raise the wards using dragon fire from all six dragon dens. When a wyvern attack threatens Aretia, Violet successfully enacts the wards but discovers they are still faulty. She also learns that Xaden has a secret second signet, one that allows him to read people’s intentions before they act. General Melgren and General Sorrengail summon Violet and the Assembly to meet with them. Melgren, who can see future outcomes, predicts that venin will overrun Samara and requests aid from Aretia. Brennan denies the request, and General Sorrengail, shocked to learn Brennan is alive, hands over Lyra’s journal, believing Violet will uncover how to activate the wards.

Xaden and Violet begin to rebuild their relationship after agreeing to be more truthful with one another. Jesinia continues translating Lyra’s journal. Violet realizes that venin gathering near Samara are a distraction, and someone inside Basgiath plans to sabotage the wards. Violet and her supporters fly to Basgiath to defend the wards against the advice of Aretia’s Assembly. By the time they arrive, Jack Barlowe—revealed to be a venin—has destroyed the wardstone, breaking the wards. With the majority of their forces in Samara, General Sorrengail and Basgiath’s leadership devise a battle plan against the approaching wyvern hordes. Violet’s squad is tasked with guarding the wardstone while Brennan attempts to repair it using his signet.

As the battle begins, Violet uses her lightning powers to protect her squad. Sawyer loses a leg to a wyvern, and while Violet is delivering him to healers, she is attacked by several venin, only to be saved by Andarna, who breathes fire for the first time. Jesinia arrives with the newest translation of Lyra’s journal, which reveals that seven dragon dens are needed to complete the ward ritual. Violet realizes that Andarna, with her camouflaged scales, is from the seventh den, Feathertales. As Violet gathers the seven dragons for the ritual and begins imbuing the wardstone with power, it is taking her life. Violet's mother comes and sacrificies herself, dying in the process. Xaden continues to fight the venin, confronting the venin Sage who has stalked his dreams. In order to save Violet, Xaden channels the earth’s power and turns venin. 

Thanks Super Summary for helping me remember what else happened. 

https://www.supersummary.com/iron-flame/summary/?searchId=b114e15c-febf-4eec-9db2-826486cfe0ac&searchPosition=1