book about girls and kidnapping

[jessicaland]

i read a book a few years ago about 2 younger girls, teenaged i think, who go to live in a different city and end up solving a kidnapping. they use alias' and their dad used to tell them that an intelligent man could read the newspaper without moving his lips. one of the girls also rushes home from school to delete a message off of the answering machine. i think the girl that was kidnapped was the mayor's daughter but i'm not sure. does anyone know this book? i have been trying to think of it for months.