What to remember from 'Iron Flame' before Rebecca Yarros releases 'Onyx Storm'

• The third book in Rebecca Yarros' "Empyrean" series comes out on January 21.
• It will pick up where dragon rider Violet Sorrengail left off in "Iron Flame."
• Warning: This article contains major spoilers for "Fourth Wing" and "Iron Flame."

The much-anticipated third installment of Rebecca Yarros' "The Empyrean" series is finally hitting bookshelves.

"Onyx Storm," which continues Violet Sorrengail's journey to become a dragon rider, will be released on January 21 by Red Tower Books.

Yarros' dragon-filled romantasy world became massive in "Iron Flame," and it might be difficult to remember everything that happened in the sequel before you read the third "Empyrean" book.

Check out Business Insider's recap of the major events in "Iron Flame" so you're ready for "Onyx Storm." And if you need a refresher on the first installment in the series, you can also read BI's guide to "Fourth Wing."

The rest of this article contains major spoilers for "Fourth Wing" and "Iron Flame."

Violet Sorrengail was reckoning with some major shocks at the start of 'Iron Flame'

When "Iron Flame" opens, Violet Sorrengail is recovering from a battle that brought her face to face with venin and wyverns, evil creatures the government of Navarre — including her mother, General Lilith Sorrengail — told her weren't real.

The battle also revealed that her romantic interest, Xaden Riorson, and other students at Basgiath, the war college Violet attends, have been secretly fighting for the revolution, and it left her friend Liam dead.

As if those revelations weren't enough, Violet also awakens at a rebel outpost in Aretia to discover the mender who saved her life is Brennan, her brother she thought had died. Instead, he has been working with the rebels under an alias since his disappearance.

Violet and her other classmates decide to return to the Riders Quadrant at Basgiath before the school's graduation. They are under strict orders to keep the venin attack — and the true cause of Liam's death — secret. Violet also decides to try to find information about Navarre's wards to help protect innocents from the venin.

During the fight, Violet's younger dragon, Andarna, exerted so much power to protect Violet that she escalated her growth process and had to fall into a deep sleep to complete her change. Violet takes her to the Vale, the home of the dragons, to recover while she returns to Basgiath with her other dragon, Tairn.

New dangers at Basgiath

After graduation, Xaden is assigned to work at an outpost called Samara, a full-day flight away from Basgiath. Xaden and Violet, who is still a student, must visit each other every seven days so her dragon, Tairn, and his dragon, Sgaeyl, can see each other because they are mated.

Meanwhile, the imposing Vice Commandant Varrish comes to work at Basgiath, keeping a close eye on Violet and her classmates who were at the venin battle.

Violet also discovers that Jack Barlowe, her nemesis from "Fourth Wing," whom she thought she killed, was resurrected. Violet is wary of Jack as he's integrated back into Basgiath, but when a first-year student tries to kill her, Jack saves her, telling Violet they're even after his attempts on her life the previous year.

Violet and her squad continue to bond as they face new challenges in a Rider Survival Course. Violet also manages to steal a journal written by Lyra, one of the First Six Riders, from the royal family with their help. She hopes it can offer insight into how Basgiath's wards function.

The danger surrounding Violet at Basgiath comes to a head when Varrish and his cronies torture her for five days for stealing the journal. Visions of Liam keep Violet sane during the torture. When Varrish taps Violet's childhood friend Dain Aetos to wrench secrets from her mind with his signet power, he surprises them all by betraying Navarre and freeing Violet.

Xaden arrives soon after, and he and Violet kill Varrish and confess their love for each other. They also decide to reveal the existence of venin and wyvern to the Basgiath student body, giving their peers the chance to join them as they flee to join the rebels.

They manage to convince around 200 riders to leave with them, including Dain, Violet's squad, and even some teachers, heading to Xaden's home, Riorson House, for safety. Mira, Violet's sister, also joins her siblings at Basgiath.

Violet and her squad join the resistance

Andarna wakes up soon after Violet arrives at Riorson House, and she now appears to be a large, black dragon. Though she has matured into a moody adolescent, her disrupted growth means her wing muscles didn't develop correctly. She will never be able to bear a rider, which is heartbreaking for both her and Violet.

Meanwhile, Violet and the other cadets from Basgiath settle in with the rebels. They continue to train alongside gryphon riders — including Xaden's ex-girlfriend Cat — which can be fraught as the riders learn to trust each other.

Ahead of a wyvern attack, Violet manages to get the wards surrounding Aretia up, though they don't work as well as those in Navarre. Lilith then gives Violet Lyra's journal during a meeting because she wants her children to be safe, and Violet taps her Scribe friend Jesinia to translate it so they can find answers about the wards.

During their time at Riorson House, Violet realizes Xaden has a second signet he has kept secret from everyone but her. He confides in her that he is an inntinsic, allowing him to read people's intentions — a signet that riders are immediately killed for having because of the dangers they pose to other riders.

The conversation also hints that Violet has a second signet that has yet to be revealed because she is bonded with two dragons.

'Iron Flame' culminates with a battle at Basgiath

Violet and her friends rush back to Basgiath when they realize venin are launching an attack on the school. When they arrive, they discover that Jack has secretly turned venin months ago, and he destroys the wards after killing his own dragon.

Dragons, gryphons, and their riders work together to defend Basgiath from venin and wyverns in an intense battle. Brennan manages to mend the wardstone Jack broke, and Jesinia finally translates Lyra's journal, telling Violet they need a seventh type of dragon to make them work.

Jesinia's discovery makes Violet realize Andarna isn't a black dragon as she previously believed and is, in fact, the seventh breed of dragon. Andarna then tells Violet she didn't hatch for 650 years, as she was waiting specifically for her.

The dragons assemble to raise the wards, and Violet nearly gives all her power to secure them until her mother steps in. Lilith sacrifices herself, raising the wards and killing the invading wyvern.

Violet rushes to find Xaden after the battle, and she discovers he has the red-rimmed eyes associated with the venin, as he took power from the land to try to protect Violet. The book ends with Jack telling Xaden there is no known cure to turning venin.

Violet won't continue her studies at Basgiath in "Onyx Storm," instead traveling to find allies to help fight the venin — and save Xaden.