The forest boy is mentioned at the very start of the novel. This short introduction is the book's only passage from the perspective of someone other than Kelly Clegg and the only instance of third-person prose.
The boy lives his daily life in a state of anxiety, dreading the return of Eld Stagger or his devotee, the Grim Halberdier. He has to sleep during the day because he is afraid of what the curse will do at night. But the children, with their song, do not let him sleep.
When Kelly is searching for Emma Lee, the boy appears to her, seemingly moving in and out of sight at will. He guides her in the direction of the girl and Momma Kodi, but he disappears shortly after that.
Noting the boy's emaciated appearance, Kelly prepares him a lunch the next afternoon and heads into the woods, where he appears to her. He tells her that she had been the one to bring the bear to the woods. He also informs her that Anvilback had brought Emma Lee from the cursed portion of The Green Ravine River Valley to Kodi's territory. He warns her that the curse is real and so was the Grim Halberdier.
That night, when Kelly and Garrett venture into the woods, they find the boy running across the river bed. He has either escaped the Grim Halberdier or has been running through the forest to evade him. The boy tries to tell Kelly and Garrett to forget about him and get away, but when the Halberdier appears, the two fight back and separate the boy from the phantom. Kodi's roar causes the Halberdier to retreat for now.
The boy witnesses the river battle between Kodi, Anvilback, and Drag-Belly. He refuses to leave Kodi when Garrett wants to use the distraction of the fight to cross the bridge and rescue Laylah. Garrett instead uses his talent of howling to divert the beasts' attention. The boy watches from a safe distance while Garrett and Kelly fight off Drag-Belly.
The boy follows Garrett's instructions after the fight, helping him get back up to the road so Kelly can put them in the car. After Kelly drops Garrett off at the hospital, she brings the boy home and lets him sleep in her and Garrett's bed.
The next morning, Kelly and the boy have an extended conversation where he reveals his true nature. The shadowy curse in the woods is the Biblical Leviathan, an ancient beast with a will of its own. He explains that the shadow was extracted from the darkness in the hearts of humans. The Leviathan's Father, the man who did this, was trying to cure evil. When the man discovered that much of evil had its origins in loneliness and ignorance, he separated these elements into their own living being, resulting in the boy.
The boy states that Momma Kodi and King Firehide are two other aspects of the Leviathan, just like the boy and the shadow. Eld Stagger and his thugs are invaders, and the shadow came to obey them because it gives its loyalty to whoever is the strongest. The shadow is even easier to control when Stagger has the boy enslaved, which is why the Halberdier is after him now.
Kelly, only half serious, asks if she should call him "Levi" or "Ethan." The boy accepts "Ethan."
When shown the letter written by Muriel Greaves and the sketch she drew of his face, Ethan reveals that she, like Kelly, had taken him in and showed him kindness. He ascribes Kodi's failure to appear in 1915 to the town's treatment of her at first. Then, he theorizes that one person, one woman, is connected to Kodi by way of an unfulfilled maternal instinct. In 1915, it was Muriel. And now, in 2015, it's Kelly. Ethan now believes that Kodi won't appear if the one who summoned her does not come to the woods, because in 1915 Muriel was in jail the night the Grim Halberdier tried to make his move.
The two of them plan to ensure that Kelly makes it into the woods that night, knowing that the Halberdier will try to stop her.
Ethan accompanies Kelly to Sammie's house, where Rachael calls the police on them. Sammie, influenced by Rachael's insistence that Kelly is becoming unstable, assumes Ethan is a random boy that Kelly is using as a prop. Ethan holds his ground, leaving with Kelly before the police can arrive.
Branchett leaves Kelly in the cell, as do her mother and father. Even Garrett storms off, but Kelly and Ethan doesn't know at the time that this is an act. Only Ethan obstinately refuses to leave Kelly's side until Chester Cotton forcibly takes him away, saying he'll be put in the foster system.
Garrett, having baited Cotton into thinking he was in the clear, hides outside the station and witnesses Cotton throwing Ethan into the trunk of his car. After giving a press conference, he drives with Ethan into the woods.
Kelly ventures into the forest that evening and reaches the clearing, witnessing Ethan and Cotton, now revealed as the Grim Halberdier, having a heated exchange.
Ethan first tries to convince the Halberdier that Stagger will toss him away. The Halberdier responds that he is an ancient being himself and actually knew Stagger, Anvilback, and Drag-Belly when they were all one beast. Horrified, Ethan then questions if the Halberdier is willing to defy the pale man, who once spared this world. The Halberdier's answer is that the pale man had spared the world when it was peaceful and balanced, but now it is as corrupt and violent as any other Earth he's found. As a last resort, Ethan threatens the Halberdier with the wrath of his father if the Halberdier helps Stagger destroy this world. The Halberdier scoffs, reminding Ethan that his father had voluntarily left the world, leaving the boy to his fate.
The Halberdier then ties Ethan to the twisted tree, forcing him to watch the sacrifice of Laylah. Kelly stalls the Halberdier long enough for the town to arrive.
When Momma Kodi appears, Kelly uses the distraction of the fight to cut Ethan loose.
After the Halberdier is downed by a shot to the face from Angus Branchett's Revolver, Ethan cries over Kodi's wounds. In his grief, his mind blurs the distinction between the bear and Kelly, and he begins to call Kelly "Momma." Kelly accepts this over her own fears.
On the way home, Ethan realizes something is wrong when the shadow on the ground, rather than doing its normal aimless rolling, is traveling in waves in the direction of the bent cedar tree. He runs back to the clearing, followed by Kelly and Garrett. They all witness the moment the Grim Halberdier decapitates himself to trade his life for that of Stagger.
Kelly hauls Ethan back to town, but he protests it will do no good. Garrett forces Ethan into Kelly's car, with the plan being for Maggie and Gordon to drive off with him. But by then, Stagger has already willed the Leviathan to surround Grunwald, trapping everyone.
Ethan presumably gives Maggie an earful, because she ends up using the car as a weapon to try and ram Stagger. But the elk's control of the shadow is too great--the Leviathan lifts the car and then captures Ethan for Stagger. The Eld King then holds Ethan in place throughout the rest of the battle.
After Kelly realizes that Kodi is not connected specifically to her, but to any act of maternal protection that Ethan witnesses, she understands that Ethan is the central, controlling consciousness of the Leviathan rather than the shadow. She names Ethan the only real King of the Forest.
Ethan stands up to Stagger and seizes control of the shadow in doing so. He forces it to release Kelly and Garrett before commanding it to bring back the consumed Kodi and Firehide. The two animals rush Stagger, who has been robbed of the shadow to defend himself. Although he fights back, the shadow versions of Kodi and Firehide pull Stagger to the ground and tear him in half.
Ethan then absorbs Kodi, Firehide, and all of the creeping shadow into his own body. Though he is an ancient being and he wants to remain with Kelly, Chief Branchett insists on doing things the official way. Ethan allows himself to be put through the state system long enough to be given an official record and a Social Security number.
In the final chapter, he is shown to have been adopted by Kelly and Garrett. He has taken the legal name of Ethan Levi Clegg.