1854. As the Cardiff-bound train puffs out of Paddington Station, young Hugh Kellow wraps a protective arm around his large valise. He has been entrusted with a priceless silver coffee pot, designed in the shape of a locomotive, by his elderly silversmith employer. But two of Hugh's fellow passengers are taking an enormous interest in the valise and as the journey progresses, Hugh's tongue is loosened and he tells them all about his priceless cargo. It will be the last mistake he'll make. When a dead body is discovered in a room at the Cardiff Railway Hotel, beside a large empty valise, the great Railway Detective Robert Colbeck and his trusty sergeant Victor Leeming are called in to investigate; but all is not quite as it seems.