Don't Scream! — R.L. Stine

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Jack Harmon finds a cell phone on the school bus. He raises the phone to his ear and hears a girl's voice: "Hi, Jack. Don't scream. I've been waiting for you. I'm your new friend." Jack thinks it's a joke. He tries to end the call, then turn the phone off, but the girl's voice won't go away: "Don't make me angry, Jack. I'm warning you." Jack is puzzled and a little frightened. He must obey her every wish. She appears in all sorts of electronic devices-he can't escape her. "Don't scream, Jack. I'm just a voice. But you're going to be my body." She begins to force him to do dangerous things like stealing a laptop from school. But Jack finally outwits the voice when she jumps into his wristwatch. The school bully has been after that watch all year, so Jack finally lets him have it.