Sneaking Out (Sweet Valley Twins #5) by Francine Pascal

All the kids at Sweet Valley Middle School are talking about the big Johnny Buck concert. For the second year in a row, the twins' parents say they are too young to go. Elizabeth is disappointed, but will do what her parents say. But nothing and no one in the world can stop Jessica from seeing her rock idol--even if it means sneaking out. Soon Jessica comes up with a plan that she knows will fool her parents--but it means neglecting her responsibilities. Will Elizabeth, once again, step in and take over for her sister--or will she tell her parents the truth?