First use of a new agent photo of Rollin Hand, in the I.M.F. dossier.
The map shown to Mrs. Cherlotov when she is asked to trace her escape route is actually a contemporary map of the border between West Germany and Czechoslovakia, with the border area highlighted in blue and some made-up city names (e.g., "Beoun") -- somewhat like the "Gellerese" shown on street signs and the like.
John Colicos, Michael Forest, and Felix Locher were all guest stars on the original Star Trek (1966). Colicos played Kor in Errand of Mercy (1967), Forest played Apollo in Who Mourns for Adonais? (1967), and Locher played Robert Johnson in The Deadly Years (1967).
The only story where team members return to the opening apartment.
Briggs does not actively participate in the mission. He only receives the mission details and coordinates the plan from the apartment.