It is China in 1865. Strife and rebellion rock the land. Trying to maintain order is the British Empire and the martial arts expert, the Ten Tigers of Canton. Adding to the confusion is the impossibility of many people already knowing Ian.
Continuity
Although it is never expressly identified, various clues suggest that the energy being the Doctor and his allies faced here was the Mandragora Helix, which fought the Fourth Doctor in the fifteenth century in The Masque of Mandragora; the Tenth Doctor confirmed its presence here when he faced Mandragora again in the New Series Adventures novel Beautiful Chaos.
