The narrator wakes up alone in the middle of the dark woods with no memory of how he got there.

The narrator's mother shows him a runaway note written in his name, but his name is misspelled, proving someone else wrote it.

The narrator participates in the Balloon Project, attaching his introductory letter to a balloon and releasing it from school.

The narrator receives the first response from his pen pal: a blurry photograph with no letter and no return address.

The narrator reviews his collection of pen pal photographs and realizes he appears in every single one.

The narrator receives a photograph showing him and Josh playing in the woods just the day before it arrived.

The narrator and his mother move to a better part of town; both families pool resources to buy the boys walkie-talkies.

The narrator and Josh sneak through the woods at night to search for the missing cat, Boxes, at the old house.

Josh discovers that the narrator's old bedroom walls are covered in hundreds of photographs of the narrator.

A stranger in the old house chases Josh through the building; Josh loses his walkie-talkie while escaping.

The narrator bumps into Veronica, Josh's sister, at a movie theater and they arrange a future date.

A car deliberately strikes Veronica in the parking lot while the narrator briefly steps away; the driver photographs her.

Recovering in the hospital, Veronica tells the narrator that Josh ran away from home, leaving a note on his pillow.

The narrator's mother reveals that Veronica died in the hospital several weeks after his last visit.

Josh's father unearths a buried pit in the woods containing Josh's corpse entangled with the pen pal's dead body.

The story opens with the narrator waking inexplicably in the dark woods as a child, only to discover that someone wrote a fake runaway note in his name. Flashing back, the narrator participates in the Balloon Project at school, unknowingly attracting a dangerous pen pal who sends photographs proving he has been watching the narrator from close range. After moving to a new part of town, the narrator and Josh return to the old house and find overwhelming evidence of an obsessive stalker who has been living there. Years later, the narrator reconnects with Josh's sister Veronica, only for a mysterious car to deliberately strike her down in a parking lot. Veronica reveals before her death that Josh vanished after leaving a suspicious note — chillingly echoing the narrator's own childhood experience in the woods. The truth is finally confirmed when Josh's father unearths a buried crypt containing Josh's body alongside the corpse of the pen pal who had been stalking the narrator for years.

The central mystery of the narrator's haunted childhood.

The narrator invents a game of pretending monsters chase him home before dark, developing a genuine fear of the woods at night.

After waking in the woods, the narrator steps on thorns and spots a deflated shark-shaped pool float lying on the ground.

The narrator writes his Balloon Project letter with a broken arm and tucks a dollar marked 'FOR STAMPS' inside for his pen pal.

The narrator and Josh run a snow cone business in the narrator's neighborhood; Josh accidentally injures the narrator at the machine.

While splitting their snow cone profits, the narrator finds a dollar marked 'FOR STAMPS' matching the one enclosed with his Balloon Project letter.

The narrator's mother calls the police after her son shows her that he appears in all of the pen pal's photographs.

Mrs. Maggie throws a shark-shaped pool float into the lake for the narrator and Josh to play with.

The narrator and Josh collect scrap construction material from The Ditch and build a raft to sail down the tributary.

The shark-shaped float the narrator hid in the woods for their planned expedition turns up missing before they can use it.

During a raft expedition, an unseen figure in the dark woods calls 'Hello' back to the boys after they shout out.

The raft splits in two, partially submerging the boys; the narrator's map of the woods is lost in the water.

The narrator finds his lost map returned to his pocket with two faceless stick figures and a number added to it.

The narrator waits at the movie theater for Veronica, who never arrives; an unresponsive stranger sits down beside him.

Veronica's parents receive a large phone bill revealing that hundreds of photos were sent from her missing phone to the narrator's.

Josh's father recognizes the pen pal's corpse as the man who paid him to fill holes on his property.

From the narrator's childhood game of racing home before dark to the eerie dollar marked 'FOR STAMPS' that resurfaces during his snow cone business, Penpal is filled with quietly unsettling details that foreshadow the threat closing in. After the narrator's mother calls the police upon learning about the pen pal photographs, the boys pivot to building a raft so they can explore the woodland tributary more quickly. They have their shark float stolen, encounter an unseen voice calling back to them from the dark woods, and lose the narrator's map when the raft splits apart — only to find the map returned to his pocket with mysterious additions. Years later, the narrator waits at the theater for a Veronica who never arrives while an unresponsive stranger sits beside him in the dark. In the aftermath of Veronica's death, her parents discover that hundreds of photographs were sent from her stolen phone to the narrator's, and Josh's father finally identifies the pen pal as the man who had paid him to unknowingly bury the bodies.

Hidden details and secondary threads that shaped the story.

Stranded in the dark woods, the narrator climbs a tree and uses the North Star to determine which direction leads home.

After falling from a tree and breaking his arm, the narrator's mother adopts a kitten he names Boxes to console him.

The narrator and Josh are caught sneaking into the woods at Josh's house; Josh's father insists the truth must be told.

The narrator's pet cat, Boxes, disappears while the narrator is staying overnight at Josh's house.

Inside the old house crawlspace, the narrator finds bowls of cat food, a blanket, and dead animals proving someone was living there.

A stranger uses Josh's stolen walkie-talkie to communicate that he has taken the narrator's cat, Boxes.

The narrator's mother confirms she never left anything for Boxes in the crawlspace, proving a stranger truly was living under the house.

Mrs. Maggie warns that 'Tom' is home, but the narrator mishears it as 'Mom,' failing to grasp the danger.

Men in biohazard suits carry black bags smelling of decay out of Mrs. Maggie's condemned house, implying she was murdered.

The narrator and Josh meet on the first day of school, bonding over matching lunchboxes and a shared love of cartoons.

At the narrator's twelfth birthday party, Josh tells him their friendship is strained because the narrator once 'left.'

Josh refuses a new walkie-talkie, promises a birthday gift, and warns the narrator about sleepwalking; it is the last time they meet.

A drawing of the pen pal beside a small boy with the narrator's initials is found in the pen pal's pocket.

Josh's body is found with his hair dyed dark brown and dressed in clothes too small, revealing the pen pal altered his appearance.

The narrator concludes the pen pal, unable to abduct him, chose Josh as a substitute because of their powerful physical resemblance.

The pivotal moments in Penpal often arrive quietly — in the narrator's instinctive climb toward the North Star, in the adoption of a kitten that later vanishes, and in Josh's father insisting that the truth must always be told. The discovery of signs of occupation beneath the narrator's old house is a critical revelation, confirmed when his mother admits she never left anything in the crawlspace, and made sinister when a stranger uses Josh's stolen walkie-talkie to announce he has taken the cat. Mrs. Maggie's final warning goes dangerously misheard, and the biohazard crews who later emerge from her condemned house leave the narrator to piece together her fate alone. At the novel's emotional center is the friendship between Josh and the narrator, which began over matching lunchboxes and ended with Josh's cryptic farewell at a birthday party — the last time the narrator ever saw him. The novel's devastating final revelations — that the pen pal dyed Josh's hair and dressed him in the narrator's old clothes, then died entangled with him — confirm that the narrator's resemblance to his best friend sealed Josh's fate.