On July 6, 1906, Baron Gustaf Mannerheim boarded the midnight train from St. Petersburg, charged by Tsar Nicholas II to secretly collect intelligence on the Qing Dynasty's sweeping reforms that were radically transforming China. One of the last Tsarist secret agents, Mannerheim chronicled almost every facet of China's modernization, from education reform and foreign investment to Tibet's struggle for independence.

On July 6, 2006, writer Eric Enno Tamm boards that same train, intent on following in Mannerheim's footsteps. Initially banned from China, Tamm devises a cover and retraces...