A businessman discovered a wormhole to the 17th century China. Having gathered enough funds through cross-time trading, he put together 500 like-minded individuals for his conquest of the past. With a shipload of modern materiel and equipment, they carved out a fiefdom for themselves, in the county of Lingao, Hainan Island, Ming Empire.
The five hundred up-timers came to be known as the Lingao Senate, wielding absolute power over the down-timers, or “natives”. Because of their power, and their utopian vision ( at least by some "senators"), coupled with their imitation of 20th century methods of government, the time-traveller's empire often seemed dystopian.
It's not a book written by a single author, under a well-thought out storyline, instead, under the theme of "time travel", 500 forum members (who play as 500 senators) each wrote their own stories about what they might want to achieve in the 17th century, and the author compiled these plans and (often dark) fantasies into a book.
Because the professional background of each senator varied, from ship-making and weapon-making, to steel-melting, to cattle-raising, to brothel-opening and spying, the resulting book seemed like an extremely detailed guidebook for how to re-create modern technology and society in the 17th century.
The charm of the book lies in these technological details. In the passage about making dynamite, Jules Verne's method in his classical sci-fi The Mysterious Island was mocked, and replaced with a more realistic method. As a trade-off, the book often seemed too tech-savvy, with the story slow and incohesive.
The other positive attribute is that the authors had no qualms about portraying themselves as the con-men, with lofty ideas coupled with Machiavellian methods. Often, their methods drew mocking references to 1984, or to the Chinese practices during Mao Era. It's part of the reason why the book got temporarily banned in late 2019.
Illumine Lingao is meant to be a break from earlier (2000s and 2010s) Chinese genre of time-travel fictions, whereas the standard storyline is that the hero travels alone back in time, to a period when The Chinese Empire was under threat of the foreign invaders (Mongols or Whites), and single-handedly saves the empire. Or, if it's a female time-traveler, she often involves herself in a romantic affair with a Qing Prince, defeating competitors. Illumine Lingao tries to be realistic in tech-details and human motives, and is lauded for that.