Reflection in a Dead Diamond (1970)

John D, a septuagenarian living in a luxury hotel on the Côte d'Azur, is intrigued by his roommate who reminds him of the craziest days of the Riviera during the 1960s. At that time, he was a spy in a growing world full of promise. One day, this neighbor mysteriously disappears... and brings John face to face with his demons again: are his adversaries of yesteryear back to sow chaos in his idyllic world?