Jo Salis is a freelance agent.
His activities which have been documented take place during the Russo-Japanese war, a conflict started by Japan when negotiations to essentially divide up controlling influence in northern China broke down. Put simply, Russia wanted the warm-water port known then as Port Arthur, now at or near Dalian, China, which it was 'leasing' from China and Japan feared Russia might try to hinder its expansionist plans in Korea and other parts of China. When talks broke down in 1904, Japan attacked Port Arthur and the war was on. A peace would be brokered the next year aided partially by the actions of American president Teddy Roosevelt for which he would receive one of the first Nobel Peace Prizes.
The opening paragraphs of one of those stories set the scene nicely concerning Salis:
"There is no one better known throughout neutral territory than Captain Jo Salis, the British spy who has served on both sides in the Russo-Japanese war. Three years ago, young Jo was just one of the Shanghai boys; always more ready to spree than work, and fickle as the wind that blows over the winding Whangpoo [a man-made river flowing through Shanghai].
"Soon after Jo was of age, war broke out, and with war were vistas of fortune for all on the China Coast. Joe was eager to go north; his father was willing, for the son could sign chits more easily than his parents could pay them when compradores brought them to the modest terrace-house in the Bubbling Well Road. Thus Jo quickly got the change which was to be his opportunity. He burst meteor-like on Tientsin, with five hundred dollars to his credit, and no debts."
We will learn from other sources and testimonies that Salis was born and raised in Shanghai, had a "smattering of the five languages of the China Coast; in each it was easier to spend money than to make it". We also discover quite quickly that Salis' primary, and likely only, goal in his involvement in that War was to make money so his lifestyle could be maintained. We are told by one commentator that "he transfers his services from one side to the other, and is none too careful to end the old employment before beginning the new".
While his duplicity seems less than honorable, his bravery, if you will, and his audacity are noteworthy. "There is no enterprise too dangerous for him if only the pay is good enough, and not one of his astonishing exploits but is followed by a still more astonishing escape."
One reviewer gives us the opinion that "his adventures, as numerous as they are daring, fail, however, to excite one's keen interest because, with one's sympathies untouched by their central figure, one cares but little how they end". That commentator does marvel, though, when "he succeeds in winning the affection of a beautiful American girl, who, with her father, is exhibiting a novel taste in holiday-making by endeavoring 'to see the war'".