The Curious Coronation — Carolyn Keene

When Louise and Jean Dana are sent eight invitations to the same pageant competition, they think it strange. But they have no idea that it will launch them on their most intriguing mystery yet. First of all the jewelled crown to be worn by the winner of the pageant is stolen, and then one of the contestants is kidnapped. After receiving a strange message, Louise and Jean embark on a rescue attempt, but as they set out they cannot imagine the terrible danger that awaits them.