For the first time, see Katie's fifth through eighth mysteries together in one volume! First, in the Great Twin Mix-Up, Katie's sister Cathy is kidnapped by the twin of Carol's best friend. Then, in the Golden Egg Mystery, Katie's Christmas gift to her mother is stolden right out of her shopping bag. In the Case of the Missing Rookie, a trip to Cathy's prospective medical school results in a mystery involving a campus-wide conspiracy and a missing student. Finally, in the Mystery of the Vampire, there's a serial killer loose at the high school, and he has the M.O. of a vampire, leaving Katie to prove that such creatures don't exist. And last but not least, in this volume, you'll find a special short mystery story from the perspective of Carl Carter, Katie's youngest sibling and mystery-solving sidekick - Carl and the Missing Valentine Mystery!