From Wikipedia:
The Night Revels of Han Xizai is a painted scroll depicting Han Xizai, a minister of Li Yu. This narrative painting is split into five distinct sections: Han Xizai listens to the pipa, watches dancers, takes a rest, plays string instruments, and then sees guests off.
Gu Hongzhong was supposedly sent to pry on Han Xizai's private life per emperor Li Yu's request. One theory is that Li Yu wanted to know why Han refused his offer to make him the prime minister. Another is that Han Xizai repeatedly missed early-morning audiences with the emperor because of his revelry, fondness of drinking and banquets with friends, and needed to be shamed into dignified behavior.
The work was not only a painting about personal life, but also represented many features from that period. Using careful observation, all of the details of the Night Revels were thoroughly exposed and peoples' expressions were vivid and true-to-life. In the picture, there are more than 40 figures—all lifelike and with different expressions. The painting represented the lifestyle of the ruling class of that time indirectly. The painter's surprising observation of Han Xizai makes the painting thought-provoking.