Very few things have stopped Uber in its quest for world domination -- except Didi, the Chinese ride-hailing startup that in August announced it will buy Uber's China operations. This week Lulu Chen and Brad Stone tell the story of how Didi rose to prominence, and the battles its founder Cheng Wei waged to defeat dozens of Chinese rivals before taking on Uber. Now that it's conquered the world's largest ride-hailing market, can Didi finally make money?