In the cursed Town of Nowhere, Bob reveals that the most terrifying being is Thirteen, a mysterious girl who never ages and seems to exist outside of time. Feared by everyone, she possesses supernatural powers strong enough to make the moon disappear when she is angry. After confronting Bob for exposing her secrets, Thirteen becomes unexpectedly fascinated by Doom, Bob’s young nephew who has just arrived in town, and decides she wants to know him better.

Thirteen asks Doom his superpower; he says he has only a superburden — his luck. A flashback shows his parents — a racecar champion and a master chef — destroyed by his birth: his mother chose death over raising him; his father named him Doom and drove off a cliff. Thirteen welcomes him: “The golden phase of your life is over.”

Doom walks to market; every animal on the road stops to stare. A vampire and a zombie attack him — then he wakes screaming in bed. Thirteen is standing at the foot of it, smiling, reciting the nightmare back to him. She laughs a laugh that isn’t a child’s, and isn’t human.

Bob realizes Thirteen has marked Doom. He shows him a photo album where his family has been erased into silhouettes after Thirteen looked at it. They try to flee Nowhere: the car dies, then the bus they catch swerves into a tree and bursts into flames. A small figure steps out of the fire.

Thirteen walks unburned out of the flames. Bob begs her to spare Doom. She crouches to his eye level and offers something she’s never offered anyone — friendship — because she wants to see what fate dares throw at her with him by her side. Doom looks at her hand, then says “No.” Thirteen’s smile vanishes.

Gordon names himself Guardian of Nowhere and vows to end Thirteen's reign — then vanishes, visible to no one but Doom. When Bob tries to warn Doom the green stranger is the worst kind of bad news, Gordon possesses him and rewrites the warning into praise, blessing the boy as Nowhere's chosen one. Then a goblin rings the bell with a black envelope: Doom has been accepted into Raven Heights Academy.

Raven Heights trembles before Doom even arrives. Sister Gazala, a nun who prays to the Devil, and Principal Crowe, cursed to burst into flames if he leaves the school, plot to drive the unlucky boy out before he ruins them. As a class whispers that saying "Thirteen" three times summons her, Doom knocks three times at the door — and Gazala bars him as an upside-down crucifix cracks in two.

Turned away from class for being late, Doom meets Ernie — a jealous, oddball girl strangely drawn to the "king of misfortune." An alarm empties the school in seconds: Thirteen has come. Only Doom and Ernie stay behind as the lights die row by row and the girl appears in the dark, smiling at them both.

Enraged that Doom called Ernie his friend after refusing her, Thirteen traps him in a vision of drowning in lava — but he snaps free and stands his ground. She vows to teach him what real fear is, then forces her way into Doom's class by threatening to burn the cursed school down. Terrified Principal Crowe caves: now his tormentor has a student ID.

Ernie decides to befriend Doom, betting his extraordinary bad luck will finally rescue her boring life. But Thirteen is now installed in the classroom, and she conjures a phantom snake that bites Doom without leaving a mark, getting him thrown out. As he flees, she leans toward Ernie with a quiet verdict: no one is allowed to be Doom's friend.

Doom refuses to go back to school — until a grizzly bear appears at the door with a note from Thirteen threatening to eat Bob. Bob shoves him out, and on the road monsters surround him and press a claw to his neck. He shuts his eyes, and opens them in a dead grey valley where Gordon stands waiting.

Gordon shows Doom a grey world beyond space and time where Thirteen cannot reach him, then refuses to let him stay: his bad luck would ruin even this place. Sent back to Raven Heights, Doom tells Ernie that Thirteen sent monsters after him — and Thirteen is already behind them, promising a dinosaur instead. She rests a hand on Ernie's shoulder and calls her a new friend.

Ernie admits no one is forcing her: she cut a deal with Thirteen and is serving a friendship trial period. Doom warns her that Thirteen is a liar, never seeing Gordon listening a few feet away. Gordon then digs a gnome statue out of the soil and kneels — his Master knows he sent the monsters himself, and wants to know how soon Thirteen will be gone.

Gazala marches her class into the enchanted forest and swears the clearing is safe. Thirteen steals Ernie's voice with a single look, Gordon flees rather than be seen by her, and something in the black trees begins to growl.