The Ballad of Falling Dragons by Sarah A. Parker

Here is a summary with spoilers for The Ballad of Falling Dragons by Sarah A. Parker

The prologue talks about the fall of Slátra, who crashes from the Moonplume moon into the world below. She emerges from the impact site wounded and attempts to reach Arithia before she is captured, imprisoned beneath a mountain, and tortured. The Creators observe these events while recognizing that Caelis, a god with immense power, has also been imprisoned. 

In the present day, Kaan gathers the shattered remains of Slátra beneath his fortress while searching for the scattered moonshards. He is also still very worried about his mate Raeve, and is still wanting to fully protect her, especially after her recent fight.  He also learns that his alchemist, Roan, has been imprisoned in Bothaim for allegedly stealing the Book of Voyd. A young miskunn warns Kaan that multiple moons are destined to fall simultaneously. In response, Kaan opens his mountain fortress to refugees and sends warnings across his kingdom so others can prepare for the approaching disaster.

Meanwhile, Princess Kyzari remains imprisoned beneath the fortress of the Scavenger King. While she knows it was her mistake that put her there, she wants nothing more than to get out and is trying to thin of any way to escape. After receiving an unexpected reply to a letter she originally addressed to her deceased mother, she begins constructing a lockpick in hopes of escaping. At the same time, Kaan's sister Veya secretly enters Arithia, where she discovers Elluin's hidden diary. The journal reveals that Kyzari is not Tyroth's daughter, but the daughter of Kaan and Elluin. Veya escapes with the diary while witnessing the deaths of several companions and narrowly surviving attacks herself. During her escape she becomes stranded in the mountains with serious injuries while protecting the information she recovered.

Also trapped, in a icy tomb, is Raeve, this time by her mothers doing. She also is fueled by revenge and anger, she remberes her friend Essi who has died and wants to get out to exact her revenge. Though on her escape she is reminded ofo her more deadly side “the Other”. It takes over her mind temproarily and shows her a memory. She is taken back as a dragon, she is protecting an egg, her egg tha is hatching, but it is also right in the middle of a battle. After the dragons sees her baby she knows they were meant to be together. Raeve comes back to her senses and can only think that the daughter of the dragon would be sad to see what her mother has become. 

Raeve manges to escape then travels to Bothaim intending to kill the bounty hunter Rekk Zharos for torturing the young Moonplume dragon Líri. She discovers that her violent alter ego, known as the Other, has already killed him. After disposing of his remains, Raeve receives Kaan's warning about the approaching moonfalls and agrees to meet him at Beluhn, asking only that he be there in person. Raeve does find it odd that she finally hears from her mate and she doesn’t want to run to him; she knows that her bloodlust and “The Other” are close to her. 

Meanwhile, Kaan and Pyrok infiltrate Roan's trial disguised as Runis in an attempt to rescue him after he is sentenced to death by the Tri-Council. Raeve does arrive to help with the mission. During the rescue, Raeve uses Rayne's language to force an anthe to retreat and successfully steals the Book of Voyd. Roan destroys part of the Citadel wall using a blood rune, allowing everyone to escape while Rygun defends them from pursuit. Their actions make them enemies of the Tri-Council. At the end the bloolust for Raeve is too high, she runs away to be with herself and figure it out without harming anyone else. Kann, though wanting to help, promises to stay away. 

At the same time, Tyroth captures Veya, tortures her, and restores memories that had been sealed away through Mindweft magic. Veya learns that she unknowingly poisoned Elluin's family while under mind control and that her memories were erased afterward. Tyroth also reveals that he knows about Elluin and Kaan's relationship. Bharon, Tyroth's imprisoned Sabersythe dragon, recognizes Veya, breaks free of captivity, carries her away from Arithia, and dies during the journey north, becoming a new moon in the sky.

While staying in Beluhn, Raeve begins recovering memories from Elluin's life. A traumatic memory causes her to dissociate and attack Kaan before recognizing him again. She confirms that Elluin continued to love Kaan, allowing him to realize that Elluin's farewell message had been written to protect him rather than reject him.  

Kyzari is still trying to figure out how to escape, but she is being watched carefully. Eventually the Scanvenger King comes for her to torture her. He brings a lbeloved animianl of hers, and kills her in front of Kyzari. 

Soon afterward, the dragon Líri arrives and attacks Raeve before Raeve climbs an enormous pillar of ice to remove the saddle that Rekk had used to control the dragon. Líri saves Raeve after she falls, and the two form a permanent bond. Raeve spends several days living alongside Líri in the mountains, becoming increasingly feral, until Kaan successfully reaches her and grounds her through conversation. During another expedition, Slátra temporarily takes control of Raeve's body, retrieves another moonshard, transfers part of her own life force into a Bhoggith egg, and tells Kaan that Raeve's remaining truths still exist within Slátra's memories.

Kaan also refelcts on the memory of when his sister gave birth to his niece, and how traumatizing the whole ordeal was. 

Veya continues to be torutred, especially mind torutre trying to get information, the Svanvnger King comes in, and he even tries to break her. But she is prepared and wants to protect Kaan. They throw her into a cell, only to her suprise to find her cell mate is Kyzari; and she is not looking good. 

Later, Raeve receives blood-bound orders to kill a silver-haired child hiding inside a Fade outpost. Instead, she discovers Ahvi, a nine-year-old Mindweft protecting a Moltenmaw egg. He also has some incredible powers. Raeve rescues him, rather than killing him, and Ahvi later performs a dangerous ritual using blood magic and the Book of Voyd to restore Raeve's body to its condition before Sereme's blood bind. The process nearly kills her, but Raeve willingly binds herself to the Book of Voyd, breaking Sereme's control over her. 

Before the group can recover, Sereme captures Kaan after threatening Kyzari's life. She admits that Raeve had been used as bait to lure Kaan into captivity. Kaan drinks a potion that suppresses his abilities and is delivered to the Scavenger King while Raeve and Ahvi remain unconscious.

Kaan and Raeve awaken imprisoned by the Scavenger King, Arkyn. Arkyn reveals that he is Kaan's illegitimate half-brother and reads Elluin's (Raeve’s old self) diary aloud to both of them, exposing Elluin's relationship with Kaan and confirming that Kyzari is their daughter. Kaan never knew that he had a daughter, nor that Arkyn was his brother. Raeve also learns that she originally died while giving birth before eventually being reborn. Arkyn burns one of Kaan's treasured keepsakes (a bead that is in his hair put there by Raeve), tortures him in front of Raeve. To get Arkyn to stop hurting Kaan and Kyzari, Raeve will do anything, so she submits and is forced back into the fighting pits under her former title of the Fire Lark. Raeve defeats a razah alongside Slátra before participating in a staged duel with Kaan. Instead of killing one another, Raeve attacks Arkyn's balcony using the combined powers of Ignos and Bulder while Rygun crashes into the fortress. Arkyn escapes on Elding Bird as the first moonfalls begin.

Kaan pursues Arkyn through the Moving Mists aboard Rygun. During the battle, Arkyn's Elding Bird severely injures Rygun before Rygun destroys it. Kaan catches Arkyn, recites the crimes he committed against Raeve, Kyzari, Veya, and Rygun, and kills him. Afterwards he remains beside the injured Rygun until Ahra, a Great Silver Sabersythe newly bonded with Grihm, arrives to help. At the same time, Veya escapes with Kyzari from the collapsing prison. Kyzari begins singing to Caelis, whose essence has been imprisoned within her diadem. Caelis manifests physically, heals Kyzari's injuries, and embraces her. The immense power released by their reunion causes moons to fall from the sky and fractures the surrounding landscape.

Raeve rides Líri through the violent disturbances to reach Kyzari. After Caelis silently accepts her presence, Raeve embraces her daughter, causing Kyzari's song to end and the moonfalls to stop. Kyzari briefly recognizes Raeve before losing consciousness in her mother's arms. 

Later, Raeve experiences the final memories preserved within Slátra. She witnesses Elluin giving birth to Kyzari before Tyroth murders her, rips her daughter from her chest, and places the diadem containing Caelis onto the infant. Slátra carries Elluin's body into the sky and transfers part of her own cosmic essence into it, creating the conditions for Elluin to eventually be reborn as Raeve.

Following the battle, Raeve awakens beside Kaan and Kyzari beneath the mountain, where the family is finally reunited. Ahvi rests nearby with the Fate Herder watching over him. Raeve repairs Kyzari's broken toy and places it beside one of Kaan's keepsakes. In the south, Sereme retrieves Arkyn's body and prepares another binding ritual. 

In a epilogue a white-haired man approaches Sereme and she identifies him as Haedeon Neván, Elluin's brother, who had long been believed dead.