Pascal Décosterd was a young Swiss diplomat sent to Tehran in 1979. Today, recently retired, he is embarking on a journey to try to understand the events of which he was one of the actors. Flavio Meroni was number 2 of the Swiss Embassy in Iran, today he is writing a book on negotiations to free the hostages. In their company we visit places in the United States, Iran and Switzerland, we meet the protagonists and retrace the different stages of these three years that shaped a new global balance. Behind the scenes of these events, where small and great history mingle, Ambassade offers insights into the importance of the human being at the heart of major diplomatic mechanisms.