From the back of the book:
French Indochina, the jewel of the French Empire, witnessed a time of extreme turmoil and political foment in the first half of the 20th century. As foreign imperialists struggled to maintain their precarious grip on the region, the people of the land worked to overthrow their tormentors. While the world seethed with conflict and change, hidden entities from far off in time and space took root in the jungles, gained footholds on the beaches and found supplicants in the cities. Some of these entities offered the temptation of enlightenment and power to those who could free their eldritch secrets. Some of these entities offered their supplicants great destructive powers.
Journal d'Indochine is a set of scenarios and campaign resources for the Call of Cthulhu 7th Edition roleplaying game set in French colonial Vietnam (~1925 to 1955).