Murder on the Minnesota - Conrad Allen

Temporarily forsaking the Cunard Line to work as private detectives aboard the Minnesota, a combination freighter and passenger ship owned by the Great Northern Steamship Company, George Porter Dillman and Genevieve Masefield are eagerly anticipating the prospect of a cruise bound for the Far East. As the voyage gets underway, it's smooth sailing, and George and Genevieve are hoping that perhaps this will be their first uneventful cruise. Unfortunately, their luck turns quickly as a fiery Catholic missionary is murdered in what proves to be the first in a series of crimes that will stretch them to their limit.