If you're interested in learning more about Du, I recommend the biography of General Joseph Stilwell (Stilwell and the American Experience in China: 1911-1945) which covers the political rise of Chiang Kai-shek and his thrall to Du. Stilwell, as the senior American military officer in China, was constantly frustrated by Chiang's connections, obsessions, and obligations to underworld and warlord figures, and the book covers these intrigues very well.