When Heavenlight is twenty-five, the Emperor dies and Little Phoenix succeeds him, the imperial succession generally being decided by politics rather than birth order. Heavenlight is sent to a nunnery, as is usual for concubines of dead emperors. She is brought back, however, on orders of the Empress. The imperial marriage between Little Phoenix and the Empress is an unhappy and childless one, and Little Phoenix much prefers his chief concubine, the Resplendent Wife, Xiao. Heavenlight is meant to distract the sovereign away from Xiao. The scheme backfires, Little Phoenix prefers Heavenlight, and Xiao and the Empress are both deposed and eventually executed. At age thirty-one, Heavenlight becomes Empress Consort of China.
As Empress Consort, Heavenlight is an effective administrator, much more so than her husband. She produces four sons and one daughter that live to maturity. The first son, Splendor, dies before his father. The second son, Wisdom, plots to overthrow his parents, and so he is exiled.
When Heavenlight is fifty-nine, Little Phoenix dies and the third son, Future, succeeds to the throne. Heavenlight is dissatisfied with Future's conduct as Emperor. After just a few weeks she removes him and installs her youngest son, Miracle. The new Emperor has no desire to run a country, and everyone knows that Heavenlight is the real ruler. When Heavenlight is sixty-six, she does away with all pretense and, her son gracefully abdicating, she becomes the only reigning Empress in all of Chinese history.
Heavenlight reigns as sole ruler for fifteen years, managing both the Empire and quarrels within her own family, notably between her own direct descendants and her father's grandchildren over succession rights. At age eighty-one, when she is overthrown in a coup (and her young lovers slaughtered), she loses the will to live; she dies later that same year.
I've left out Western calendar dates in this account of the life of Empress Wu Zetian, not only because they would have been anachronistic in this context, but because they would cause eyes to glaze over in all but a few history buffs. During the period the novel Empress covers, Western Europe was a cultural and political backwater and the most powerful Christian state was the Byzantine Empire, itself much weaker than it had been a century earlier. Heavenlight's lifetime occurred as Western Civilization was at its most globally inconsequential, its absolute nadir. In contrast, Shan Sa has shown us the world of the political and cultural rulers of China, at that time indisputably the world's most powerful civilization.
Shan Sa and translator Adriana Hunter (Empress was written in French) have Anglicized most of the Chinese names, leading to some entertaining hunts as I compared the goings-on in the book with the historical record as interpreted by Wikipedia. The two matched quite closely; everybody in the novel is a major historical figure, and it is fun to identify Heavenlight, Little Phoenix, Splendor, Wisdom, Future, Miracle, and so on.
It was fascinating to see the very alien conceptions of morality in the imperial Chinese court, both sexual and otherwise. Starting with sex: Of course there was a double standard, and the Emperor could bed as many concubines as he pleased while the Empress couldn't fool around with men. But it wasn't perceived this way. Heavenlight did not have to stifle jealousy when Little Phoenix bedded other women. It wouldn't have occurred to her to feel jealous; there was never any expectation of male monogamy. It's worth noting that for Heavenlight to take female lovers was never frowned upon, and once she was no longer capable of conceiving a child, taking sturdy young men into her bedchamber was practically encouraged by the Court, the better to keep her strong and youthful.
As for other sorts of morality, let me just say that to succeed in the environment in which Heavenlight thrived, you have to be, to use highly anachronistic language, extremely badass. Several times in the book Heavenlight commits acts that, in another time, another context, would be considered evil. Was she an evil person? That's probably for others to decide. But you don't become the only Empress Regnant in all of Chinese history by being a nice old lady.