This would appear to be George Christopher Willis (1889-1973) a Canadian missionary in China (1921-49) who wrote I was among the captives: Life in a Japanese Concentration camp (Singapore: Christian Bookroom, ?1946). He is easily confused with his son, a medical doctor of the same names (1923-2012) who served, for a time, in Borneo. I assume it was the older GCW who revised and slightly abridged Andrew Miller's "The Brethren" Commonly so-called: A Brief Sketch, which was published from the Christian Bookroom, Kowloon, c.1963. In the introduction, if my memory serves me correctly, the editor noted disapprovingly that Open Brethren still fail to 'judge the Bethesda question'. There is a biography of the older GCW (1889-1973) by William A Willis, Unless a Grain of Wheat (W.A.Willis, 2014). To confuse us still further there is a third generation GCW, who is a physician working in Singapore. See https://sites.google.com/site/virtualclinicofdrgcwillis/home/personal-history. I would gladly learn more from better informed correspondents! Timothy Stunt
There is a fascinating autobiography of this GCW's mother, AF Willis, which tells the story of her remarkable life having emigrated from England, then to Canada, and finally to China. It also contains observations of Darby's visit to Brantford in the 1870s. And also the astonishing life challenges of frontier life during that time! https://www.amazon.com/Days-My-Pilgrimage-F-WILLIS/dp/B017KYP9UY
PS and something of GCW in early years, hence adding the comment here.