When the residents of Moose County, including the reclusive millionaire, Jim Qwilleran, board the old steam locomotive - the celebrated Engine No. 9 - on its inaugural journey, little do they know that this first trip will also be the last. By next morning, Qwill discovers that the affluent owner of Engine No. 9, Floyd Trevelyn, has disappeared, along with his glamorous secretary and millions of dollars belonging to Moose County investors.

While the search is on for the fugitive, Qwill stays in Pickax and probes another mystery - why has Koko developed a sudden interest in certain works of literature and started to steal black pens?