In the Spider's Web(1973)

Professor Algeras becomes the target of foreign agents working for major powers, who use every legitimate and illegitimate means at their disposal to try to get hold of his scientific discovery. The most ruthless and unscrupulous foreign agent, who ultimately traps Algeras, is Milko, who comes from the countries behind the Iron Curtain. It eventually transpires that Milko, who has been brainwashed, was the professor's only son, lost during the communist child abductions.