Sammy Jacobs wishes he were invisible because his parents never seem to want to spend any time with him. Sammy’s parents, who are scientists, always admire and praise Sammy’s brother Simon, because Simon has a very serious personality, and is interested in science and school activities. Sammy is a science fiction freak and loves anything that has aliens in it. Therefore, when he finds his bedroom window open, his homework scattered on the floor, and finds himself tripping over "nothing", Sammy begins to feel that something strange is going on.
When his friend Roxanne Johnson comes to visit Sammy, she suggests they do their class report on the ghost of Hedge House, a house that is supposed to be haunted. Roxanne suggests going to the house and videotaping the ghost for their report. Sammy soon realizes that there is either a ghost or an invisible person by the name of "Brent Green" in his room.
At first, Sammy thinks that having an invisible friend would be cool, but later he finds out that Brent is ruining his life. When he asks Brent to appear in front of Roxanne, Brent doesn’t show up, and Roxanne decides to tell everyone in school about Sammy’s make believe friend, making him a laughing stock. Things go from bad to worse at home, when Brent creates a mess out of Sammy’s room and eats half the food at home, placing all the blame on Sammy. Brent also ruins Sammy’s chance at the track race, making all the students hate him, and an incident in the library makes the librarian think that Sammy is crazy!