by H.D. Jones
Eleven-year-old Marnie Sandburg likes to make really complicated things. She's building a soap box derby racer, but she has to hide most of her work because her parents don't know she's entered to race in the Unlimited Class. Marnie's got lots of secret gizmos for her racer, including an artificial inertia generator. And now her Mom has told her she has to accept the help of an assistant . . .