Tibere (Lino Ventura) is a Soviet nuclear scientist who comes to London with a platoon of his colleagues for a conference. When he is injured in an auto accident, he gets separated from them. The accident was a set-up by British MI5 (secret service). It turns out that he is a Frenchman who was kidnapped by the Soviets many years before. The British insist on his returning to the West to helping the British and French spy agencies. They don't look after him any too well, however, and he ends up being chased by everybody under the sun, including the KGB.
Source : allmovie.com