The Hardy boys and their father solve a mystery involving inexplicable crashes of high-speed race cars being used to test an experimental turbine motor.
Who is writing threatening notes? How could anyone get into the secret room of the old mansion? As Frank and Joe investigate, robbery and mistaken identity complicate matters.
False robbery charges, Joe's disappearance, and other strange things occur when Frank and Joe set out to retrieve their father's important papers from a diver.
Lettuce Leef and Nimble Charlie, the Crook Catchers to the Queen, investigate the disappearance of the queen's recipe for minestrone soup--as well as her clothing.
Nancy Drew and her friends Bess and George decide to investigate when they notice a lot of the performers with the circus are missing costume pieces and props.
When Allie is contacted by the ghost of a dog, she and Dub investigate the surly new boy at school and his father, who may be running a puppy mill, to see if they are involved.
