Der Monat der fallenden Blätter (1968)

When British philosopher Harold Hilliard took off for Warsaw to lecture on the Dysteleological Surd, he had no idea that he would soon become embroiled in international espionage. During the trip he tried to open a suitcase he mistook for his own. When a fellow passenger, a Pole with stainless steel teeth, took umbrage, Hilliard put it down to bad manners, but when the same man saw him pick up the wrong coat in the plane, Hilliard realized that he was suspected of spying. The party at the airport to welcome Hilliard only convinced the Polish agent that the British Secret Service was now picking its men with extraordinary cleverness. Hilliard, whose works were little known in England, was warmed by unaccustomed praise but chilled by the apparent certainty of the counter espionage people that he was a British agent whose code name was Whale.

Unfortunately the movie Der Monat der fallenden Blätter is not yet available on HBO Max.