This is the last episode of the original 1966 series, though it was not written to be a series finale.
No female IMF agents were a part of the mission.
The apartment for Barney is the same one used for him in the season six show "Blues".
Pernell Roberts previously played the main villain in Episode 4 in Season 3 The Mercenaries.
When the IMF team meets to discuss the mission, Duval the jewel expert, uses slight of hand to make a large diamond vanish, but you can clearly see the flash of the jewel between the fingers of his other hand as he drops it to hide there.