Hollow by Caroline Peckham and Susanne Valenti

Here is a summary with spoilers for Hollow by Caroline Peckham and Susanne Valenti

Ferris Creed lives in Arringfall, a mortal settlement surrounded by the Taking Trees, a cursed forest that has been steadily expanding and consuming the land. Every fifty years, the Great Hunt begins. Thirteen magical spirits live within the forest, each possessing an amulet. The Champions who enter the Hunt are supposed to find the spirits and collect their amulets, eventually bringing all thirteen to the Great Elm at the center of the forest. Whoever completes the Hunt can receive a boon from the Great Elm, and Ferris intends to use that boon to save her sister Rissa. Rissa was taken years earlier as an Offering to the forest and is presumed dead. Ferris has secretly spent years preparing herself to enter the Hunt, despite not being an official Champion. She also knows that the mortal settlements are threatened by another danger outside the forest: the Hollow, undead creatures created by the Fae necromancer Bane Crownthief.

On the morning the Hunt begins, the Taking Trees have advanced even closer to Arringfall. Ferris has been expected to accept a marriage proposal from Axel Bradey, but she has secretly packed supplies so she can enter the forest instead. When the forest opens, the trees unexpectedly seize Ferris with a vine and drag her inside. Axel tries to hold onto her and is pulled into the forest with her. He dies when his neck is broken, leaving Ferris alone among the other Champions. Colton Evast, one of the trained Champions, finds her and accepts that she is now part of the Hunt. Ferris discovers that most of the people who entered have already been killed. She scavenges supplies from the dead and helps bury some of the bodies before the remaining Champions continue into the forest.

The forest quickly proves to be hostile and unpredictable. The Raven spirit lures Champions into danger, resulting in the deaths of Tyson and Emmy. Ferris attempts to help Emmy but cannot save her. Later, the group takes shelter in an abandoned tavern called the Hunting Man. Ferris's secret book about the thirteen spirits attracts Colton's attention, and he realizes that Ferris has been planning for the Hunt for a long time. He also learns that she is looking for Rissa. The group discusses Bane Crownthief, the necromancer responsible for the Hollow. Bane was originally a Fae prince who became obsessed with power after his father refused to relinquish the crown. His necromantic abilities eventually allowed him to raise the dead, creating the Hollow that now threaten the mortal lands.

The story then introduces Hendrix, a Fae outcast moving through the forest independently. He is powerful, ruthless, and determined to win the Great Hunt for his own reasons. He has an infinity-shaped mark identifying him as an outcast and carries a history of conflict with the Fae ruling class. Hendrix encounters other Fae and the forest spirits while pursuing the amulets. At the same time, Ferris and Colton encounter a Fae man being consumed by the forest. When the Champions attempt to kill him, the resulting magic kills several people, and Ferris is forced to mercy-kill the survivors. She eventually becomes separated from the group and encounters the Bear spirit. Ferris feels an unusual connection with the creature, but Colton kills it and takes its amulet. Soon afterward, Ferris and Colton find Fae warriors fighting Hollow. Hendrix appears, pushes Colton into the Hollow, and takes the Bear amulet for himself. He then captures Ferris.

Hendrix takes Ferris to an abandoned Fae castle within the forest. He initially treats her as both entertainment and potential bait for the spirits. Ferris repeatedly tries to escape, but Hendrix uses his superior strength and the Bear spirit to stop her. Their relationship begins as outright antagonism, with Hendrix deliberately provoking her and Ferris refusing to submit to him. Hendrix tells her that he intends to use her to help locate the spirits, while Ferris insists that the spirits are not simply monsters to be killed. She believes they are intelligent beings suffering because of the curse. Hendrix views the Hunt much more pragmatically: whoever kills a spirit gets its amulet, and he intends to collect as many as possible.

Hendrix eventually takes Ferris to find the Fox spirit. Ferris discovers that fire attracts the Fox and successfully draws it toward her. Instead of allowing her to claim it, Hendrix kills it and takes its amulet. Ferris is furious with him. Back at the castle, she discovers a diary left by a previous Champion that contains information about the spirits and a rough map of the forest. She also begins hearing Rissa's voice and seeing strange figures in the trees. The map leads Ferris and Hendrix toward the Dragon. They travel through caves filled with Hollow and eventually reach the Dragon's nest. Hendrix ties Ferris up and deliberately cuts her so that her blood will attract the Dragon.

The Dragon attacks Hendrix and nearly kills him. Ferris frees herself and climbs onto the Dragon. Rather than attacking her, the Dragon allows Ferris to connect with it. Ferris experiences the creature's enormous grief and realizes that the spirits are suffering from the same corruption affecting the forest. The Dragon carries Ferris into the air and shows her the Great Elm and the landscape surrounding it. Ferris's connection with the Dragon allows her to claim its amulet, and her hair changes to a pearlescent silver color. Hendrix is left badly wounded, and Ferris initially considers leaving him behind. He convinces her that he knows the key to reaching the labyrinth surrounding the Great Elm, so she agrees to form an alliance with him. She carries him back toward the castle.

Hendrix begins teaching Ferris how to summon the spirits she has claimed. Ferris initially cannot control the Dragon, but eventually succeeds in summoning it. The Dragon emerges violently, destroying part of the castle and starting a fire. Hendrix protects Ferris while they escape. As they travel, Hendrix reveals more about his past. He was targeted by the Coterie, the powerful Fae group responsible for controlling and abusing others. Hendrix's family was eventually killed, and he was forced to watch. This is part of the reason he hates the Fae ruling class and has become an outcast. Ferris remains suspicious of him, but their attraction continues to grow. They also discover that their histories have a connection through loss: Ferris lost Rissa to the forest, while Hendrix lost his family to the Fae.

Ferris and Hendrix continue hunting the spirits while other Fae Champions begin killing people for their amulets. Islasees Bellatorn and his companions, Benson and Jadina, are particularly ruthless. They kill mortals and take their possessions, including the Rat amulet. Ferris and Hendrix hide from them and later bury some of the people they find dead. Hendrix becomes separated from Ferris and is captured by the Lost Children, the corrupted souls of people who were previously taken as Offerings to the forest. Their song overwhelms him and drags him toward a pit beneath an oak tree. Meanwhile, Ferris encounters the Serpent and is eventually reunited with Rissa, who appears as an adult woman.

Rissa explains that Ferris and Rissa are not ordinary mortals. Both were created through the Great Elm's magic and are spirit-born. Ferris has lived through multiple versions of the same existence, repeatedly entering the forest and attempting to break its curse. Rissa was created by the forest as part of this cycle and is now connected to the Lost Children. Ferris learns that the forest has been guiding her toward the Hunt and that her unusual ability to communicate with the spirits is not accidental. Rissa also tells Ferris that Hendrix is in danger. Ferris goes after him and finds him being overwhelmed by the Lost Children. The Dragon finally acknowledges Ferris as a Spirit Singer and uses its power to rescue both of them.

After this, Ferris and Hendrix renew their alliance and agree to reach the Great Elm together. They continue searching for spirits, but Hendrix again betrays Ferris when they find the Wolf. Ferris earns the Wolf's trust and is preparing to claim its amulet when Hendrix uses the Bear to restrain her and kills the Wolf himself. Ferris is furious because he has repeatedly taken spirits from her after she establishes a connection with them. Later, when Fae warriors attack, Hendrix protects Ferris while she pursues the Raven. Ferris finally succeeds in connecting with the Raven and claims its amulet herself. Hendrix attempts to follow her, but Ferris has had enough of his betrayals and leaves him.

Ferris's departure causes Hendrix to lose control of his power. The magic inside him begins corrupting the forest, and he stops pretending that he is simply an outcast Fae named Hendrix. He reveals that he is actually Bane Crownthief, the necromancer everyone has been fearing. His necromantic power is the reason the Hollow exist. He begins raising an army of Hollow within the forest and uses them to search for Ferris. He becomes determined to find her, both because he loves her and because he believes she belongs with him. He refers to her as his future queen.

Ferris continues alone. She realizes that her connection to the spirits is different from that of the other Champions. She finds the Unicorn and gains its trust by telling it a story rather than attacking it. The Unicorn gives her its amulet, adding another set of runes to her body. Soon afterward, Ferris is surrounded by a large group of Hollow. Bane arrives and destroys them to protect her. Ferris is overwhelmed by seeing him again and kisses him. During the kiss, however, she sees the black magic leaking from his body and realizes that the man she has been traveling with is Bane Crownthief. Bane confirms his identity.

Bane explains the truth behind his history. He had once been a Fae prince who eventually killed the corrupt Fae king. His family was then executed, leaving him devastated. His attempt to use necromancy to bring his dead family back created the Hollow. His power became known as the Blight, and the more he uses it, the more it corrupts the forest. Ferris is horrified by what he has done but remains emotionally attached to him. The two stay together, and their relationship becomes sexual. Their magical abilities interact during their intimacy, with Ferris's teal-colored spirit magic mixing with Bane's dark Blight. By this point, only a few days remain in the Great Hunt.

Bane and Ferris reach the entrance to the labyrinth surrounding the Great Elm. Other surviving Champions are also converging there. Islasees kills Princess Drava and uses her royal blood on the stone entrance, believing it will open the way. Ferris learns from the Dragon that the blood needed is actually imperial or spirit-born blood, meaning hers. Ferris uses her own blood to open the entrance. Once the door opens, a new rule is announced: killing another Champion for their amulets is now permitted. The remaining competitors enter the labyrinth, knowing that only one person can ultimately claim the boon.

Bane becomes separated from Ferris and is attacked by Benson and Jadina. He kills them with the spirits he controls and then raises their bodies as Hollow, sending them after Islasees. Ferris finds Champion Devlan inside the labyrinth and temporarily allies with him. Devlan possesses several spirits, including the Stag, Phoenix, and Carp. Their alliance ends when Islasees and the Tiger attack. The Tiger kills Devlan by decapitating him, and Islasees takes his amulets. Islasees now has more amulets than Ferris, leaving Ferris worried that she will no longer be able to claim the boon.

Ferris eventually reaches the Great Elm's courtyard. Bane is already there and fights Islasees while Ferris attempts to gather the remaining spirits. Helga, another surviving Champion, gives Ferris the Boar's amulet. Rissa arrives riding the Serpent and gives Ferris that amulet as well. Ferris places the five amulets she has collected onto the Great Elm's plinths, but the Elm reveals that all thirteen amulets must be returned by one person for the boon to be granted. Ferris realizes she still needs the spirits controlled by Islasees and Bane.

The Dragon explains that Ferris's power as a Spirit Singer allows her to communicate with and claim spirits that were taken through force rather than willingly given. Ferris calls to the spirits belonging to Islasees. The Stag, Rat, and Phoenix abandon him and transfer their allegiance to Ferris. She gains their runes, leaving Islasees with only the spirits that remain loyal to him. Islasees flees, leaving Ferris with ten of the thirteen amulets. The only remaining three are Bane's.

Bane begs Ferris to give him the remaining amulets because he wants to use the boon to restore his dead family. Ferris refuses because she intends to use the boon to free Rissa and the Lost Children. The Great Elm ultimately strips Bane's three amulets from him, allowing Ferris to place all thirteen into the tree. The curse is broken. Ferris receives the boon and uses it to free Rissa and the other Lost Children from their existence within the forest. Bane does not receive the boon he wanted. Instead, the Great Elm places a new curse on him: he must find the missing spirit Providence. If Providence is not found, the curse will eventually kill Ferris and destroy Bane through the same magical corruption.

The Lost Children are freed, but Rissa does not simply return to being Ferris's sister. She is angry about what has happened and rejects Ferris's attempt to bring her back into mortal life. Rissa takes the Serpent connection from Ferris and leaves with the other children. Ferris is left with her spirit bonds and the consequences of the boon. Bane takes Ferris with him to the Blight rather than allowing her to leave. The book ends with Ferris and Bane together in his corrupted realm, with the Great Elm's curse requiring them to find Providence.