Whisper by Phoebe Kitanidis

Fifteen-year-old Joy is used to hearing Whispers—to walking down the street and instantly knowing people’s deepest desires. She uses her psychic gift for good, to make her friends happy and give people what they want. But for her older sister, Jessica, the family superpower is a curse, and she uses it to make people’s lives—especially Joy’s—miserable. Still, when Joy hears a mysterious and frightening Whisper from Jessica’s mind, she knows she has to help her sister. Even if it means risking everything and joining forces with a boy she barely knows—a boy who may have a dark secret of his own.