Been digging in Shanghai Hongs directories kindly provided by Tess Johnston.
The mysterious Gothic mansion on 255 Anfu Lu corresponds to 297
Route Dupleix.
A large Russian family lived there in the 1930s: the 1934 directory lists Mr & Mrs W. E. Ulanoff, Mr and Mrs J. B. Cheney and B. Ulanoff. In 1936 the first Ulanoffs are still there, plus there are Mr & Mrs Leonard Corner and Mr & Mrs N. V. Rimsha. In 1939, only the "older" Ulanoffs are listed at this address. In 1941 the same two Ulanoffs are now joined by Mr & Mrs H. Rodger and Mr and Mrs S. Jooskya.
I was puzzled to see Dupleix Apartments referred to as Kingsbury Apartments in
this memoir. Mr. C. Kingsbury was living there in 1934; perhaps he was the proprietor.