Henry, Jessie, Violet, and Benny are on a train from Boston to San Francisco. Even though they used to live in a boxcar, this is the first time they've ridden a real, moving train.And they find a mystery to solve even before they leave the station. Is someone trying to steal a young woman's portfolio? Could it be the porter? Or is it the tall, bearded man who always wears sunglasses--even at night? What's in the portfolio, anyway?