The following version of this book was used to create the guide: Chbosky, Stephen. Imaginary Friend. New York: Grand Central Publishing, 2019.

Imaginary Friend is a horror novel by Stephen Chbosky set in the small fictional town of Mill Grove, Pennsylvania. It is told from multiple different third-person perspectives. The most improtant perspectives are those of Christopher Reese and Kate Reese. Kate is a widowed mother who flees from an abusive ex-boyfriend with her seven-year-old son, Christopher, in the middle of the night. Christopher and his mother have a strong bond, and Kate is especially concerned with protecting her young son from the harsher realities of the world, especially their poverty. In Mill Grove, Kate moves them into a motel while she searches for a job and struggles to make ends meet.

Christopher is more sensitive to their situation than Kate realizes, but he does still have childish preoccupations, like a cartoon franchise called Bad Cat. Over the course of the novel, Christopher loses this innocence as he becomes more aware of the suffering around him.

Christopher attends the Mill Grove Elementary school, where, one day, his mother is late picking him up. He sees a face in a cloud and wanders after it into the Mission Street Woods. Christopher goes missing for six days.

A teenage, heavily devout Christian girl named Mary Katherine sees Christopher six days later as he stumbles from the woods. Mary Katherine is obsessed with remaining the pure Catholic girl her parents expect her to be, which becomes important later to the plot. She is a secondary viewpoint character.

Though Christopher cannot remember his time in the woods, he recalls that he had the help of a man in finding his way out. He refers to the man as Nice Man. The sheriff finds no sign of any footprints besides Christopher’s in the woods. The sheriff is also a secondary viewpoint character.

After Christopher’s disappearance, miraculous things start to happen to him. Kate wins the lottery and can afford to move them out of the motel into a beautiful house right next to the Mission Street Woods. Christopher’s dyslexia and learning challenges disappear overnight, and he is suddenly the smartest in his class.

One night, Christopher is lured to a clearing in the Mission Street Woods by the voice of the Nice Man. There is a huge, craggy tree in the center of the clearing, and the Nice Man wants Christopher build a treehouse on top of it. Christopher enlists the help of his friends, Matt, Mike and Eddie, to build the structure. While they work, Christopher discovers a skeleton buried in the ground.

The trust between Kate and Christophe erodes after this episode, because he lied to her that he was spending the night at Eddie’s house, not camping in the woods building a treehouse.

The sheriff discovers that the skeleton belonged to a boy named David Olson, who disappeared fifty years prior to the main events of the novel. He has to inform Ambrose Olson, his now elderly older brother, who blames himself for David’s disappearance. Ambrose is another secondary viewpoint character. He resolves to find out the truth about what happened to his brother.

Christopher finishes the treehouse, which the Nice Man reveals is a portal to another dimension called the Imaginary side. On the Imaginary side, the Nice Man explains that an evil woman known as the Hissing Lady is trying to smash the barrier between the Imaginary and Real sides and wreak havoc on earth. Christopher, like David before him, has been chosen to stop her, as well as rescue the Nice Man from her clutches. Christopher has powers now, but the Nice Man warns that they come at a price.

The Nice Man is captured by the Hissing Lady, and Christopher must follow clues left behind by David to free him. Meanwhile, on the Real side, Ambrose and Kate make a visit to the Olson’s old house, where Ambrose finds a diary under the floorboards containing clues about what David was up to in his final days.

Christopher frees the Nice Man with David’s help, but the Nice Man cannot escape through the treehouse for good. To stop the Hissing Lady and free the Nice Man permanently, they have to steal a silver key that the Hissing Lady keeps around her neck.

When Christopher returns to the Real side, he is plagued by headaches and nose bleeds, the price of power that the Nice Man warned him about. He also comes down with a fever; every person he comes into physical contact with while he is sick also falls sick themselves, and experiences a burning itch just under the surface of their skin. Eventually the entire town is infected by the burning sensation under their skin, as it is passed from one person to the next.

Christopher falls seriously ill when he uses his powers to heal a resident of the senior care facility, but the machines at the hospital do not register that there is anything wrong with him. The doctor suggests he suffers from psychosis after Christopher tries to explain the existence of the Nice Man and the Hissing Lady. Kate, terrified that her son is developing her late husband's schizophrenic delusions, takes her son home and tries to give him the prescribed anti-psychotics. He begs her to believe him, and in the moment of the truth, she does. But as they flee town to escape the Hissing Lady, their car crashes into Mary Katherine's.

Back in the hospital, Kate joins forces with Ambrose and the sheriff to solve the mystery of the Mission Street Woods. Christopher, stuck in a coma after the accident, is trapped on the Imaginary side, where the Hissing Lady is hunting him.

The sheriff discovers tools in the woods dating back hundreds of years, revealing that Christopher and David are just two in a long line of children coerced into building a treehouse in the Mission Street Woods. The clues in David's diary lead Kate to discover that the Hissing Lady is not so evil as they thought; she is actually the only thing keeping the Devil trapped in Hell.

As Kate makes this discovery on the Real side, Christopher learns the truth on the Imaginary side. The Nice Man's true identity is that of the Devil. He tricked Christopher into building the portal and stealing the key from the Hissing Lady so that he could escape the Imaginary side and bring Hell to earth. The Hissing Lady and David have been working together to protect Christopher.

In the final showdown, Kate, Ambrose and the sheriff join Christopher and David in the Mission Street woods, where the Nice Man is turning the residents of Mill Grove into 'mailbox people' - catatonic zombie-like creatures with eyes and mouth stitched over with thread. Christopher realizes that the mailbox people only think they are trapped, when actually they have the power to drop the string and free themselves from their own inner nightmares. This releases them from the Nice Man's power, and they turn against him before ascending to Heaven. Ambrose is reunited with his brother and they move on together. Christopher escapes the Imaginary side and Kate and the sheriff burn down the treehouse to trap the Nice Man in Hell.

In the last scene of the book, the Nice Man floats over the Real side, able to watch but not interfere. He is looking for his next target, suggesting the events of the novel have a cyclical nature.