Not much is known about Emmy's origins, but it's implied she was a mistake created in a lab in the process of creating Artificial Intelligence. Emmy appears for the first time in a cellphone that Jack Harmon, the book's protagonist, finds in the bus. When Jack raises the phone to his ear, he hears Emmy's voice speaking, saying that she's been waiting for Jack, and that Jack's her new friend. Jack ignores the voice, thinking it's a joke, but when he ends the "call", Emmy keeps talking, and warns Jack to not enrage her.
Throughout the story, Emmy makes Jack do some horrible things, such as stealing a computer from his school. She keeps threatening Jack if he tells others about her.
Toward the end of the book, Jack gives a watch (with Emmy in it) to a bully, and this results in the bully turning into a digital being as well.
Emmy has a voice and a brain, but she owns no body. If anyone sees her on a screen, only her mouth is visible. In the book, she would like to possess Jack's body forever.
She can possess any electronic instrument to communicate with people, zap them, and she can even melt the electronics she's in.
- Emmy constantly says the phrase "Hi, Jack," which is likely a play on the word "hijack."