Jon Scieszka 
Time Warp Trio: Wushu Were Here [EPUB ebook] 

After being warped back to ancient China, Joe, Fred, and Anna are faced with some big tasks. They must rescue General Li Shimin from prison so he can defeat the awful ruler, Wang. Then they must figure out how to free Sam, who is trapped in . . . The Book. Join the Time Warp Trio as they learn kung fu, scale the Great Wall of China, and learn to stop time itself!