The Sage, the Swordsman and the Scholars: Trials of the Middle Kingdom 1

The Sage, the Swordsman and the Scholars is a martial arts, action-adventure, historical fantasy set in late medieval China. It is the first book of a tetralogy, blending Chinese history with sword and sorcery fantasy.
Synopsis: In the Ming dynasty, a legendary wandering swordsman and a political cabal of vigilante warrior-scholars investigate the maritime arrival of a mysterious nonhuman military force. After the discovering the truth of their agenda, measures were taken to warn the emperor of the conspiracy. He then mobilizes the army to prepare for war. However, he must first quell the Underworld where rebel groups and secret societies have risen against him. The warrior-scholars and the swordsman find themselves in service to the emperor, while a motley crew assembles to his aid. His new friend, an enigmatic sage, insists that the real battle is in fact a spiritual one, and that victory lies only through following the will of Heaven.