Marco's mother is immensely overprotective. She won't let Marco play softball with his friends, so Marco sneaks to the park without her permission.
It is at the park that Marco receives a head injury. Over the course of the next few days, Marco experiences many hallucinations as he fades in and out of many strange dreams. One recurring character in his dreams is a boy named Keith. Keith says he lives in Marco's basement, and he wants Marco to take care of him.
However, the twist ending reveals that all of the events of the book were a part of Keith's dream. Marco wasn't actually hit on the head, Keith was. Keith had sneaked out to play softball with regular kids. Keith and his mother are monsters who live in Marco's basement. The book ends with the real Marco finding Keith in his basement.
Towards the beginning of the book, Marco proves himself to be disobedient by sneaking out to play softball. Marco isn't a particularly tough kid; this is evident when Marco asks Gwynnie to help deal with Keith.
When taking into account the twist ending, some of this information becomes dubious.
The book gives almost no physical descriptions of Marco. Since Marco's sister and mother both have black hair, it's possible that Marco's hair is also this color, although it is never specified.
- Marco's father is never addressed. Additionally, the book never gives Marco a last name.
- During a dream sequence at the beginning of the book, Gwynnie's last name is said to be Evans. It's later revealed that Marco only dreamed that Gwynnie wasn't his sister. It is unknown if Evans is his last name or if he dreamed one up for Gwynnie.