Mr. Moto Is So Sorry — John P. Marquand

The 4th entry in Pulitzer Prizeâ€"winning author John P. Marquand's popular series of espionage adventures features an Australian mercenary, a Mongolian prince, and a Japanese spymaster

Eager to escape his complicated past, Calvin Gates boards a train bound for Inner Mongolia, where he plans to join an archaeological dig. Also en route to the Gilbreth Expedition is Sylvia Dillaway, a beautiful young artist with a fierce independent streak. The two Americans become unwitting players in a high-stakes game of international intrigue when Sylvia's Australian guide gives her a silver inlaid cigarette case containing a coded message. With the clouds of war looming, various factions of the Japanese, Russian, and Chinese governments will stop at nothing to get their hands on the case -- including murder.
 
Calvin and Sylvia's only hope for survival is a fellow passenger, the charming and mysterious Mr. Moto. He is Imperial Japan's top secret agent, and his mission is to ensure the safe delivery of the cigarette case to its rightful destination. To do so, he must protect the innocent Americans, but on a speeding train headed deep into dangerous territory, even his considerable skills might not be enough to save the day.
 
First serialized in the Saturday Evening Post, John P. Marquand's popular and acclaimed Mr. Moto Novels were the inspiration for 8 films starring Peter Lorre.