Like the rest of the Achtung! Cthulhu lines, a comprehensive sourcebook for what covers - in this case, World War Two Istanbul. Just as nice are the mechanics for generic espionage situations and operating in a nest of spies. The scenario is more free-form than most of the others in the line, and Keepers might need to lead players who get bogged down.

In closing, a GUMSHOE version would make it perfect!