Cyd & Shelby: Teenage Detectives is a YA (Young Adult) novel written by Shelby Marcus. It's a fictional story where Shelby and Cyd were detectives. Bret & Chet thought this was Shelby's diary. They read it and became suspicious about this and followed Cyd & Shelby. Shelby put Cyd's name in the title first because it's alphabetical.